feat: add i18n internationalization support

- Add react-i18next, i18next with browser language detection
- Support Traditional Chinese (zh-TW) and English (en)
- Default language: zh-TW, stored in localStorage
- Create 10 translation namespaces (common, auth, dashboard, tasks, etc.)
- Add LanguageSwitcher component in header
- Translate pages: Login, Dashboard, Tasks, Spaces, Workload, Audit

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/public/locales/zh-TW/audit.json

@@ -0,0 +1,56 @@
+{
+  "title": "稽核日誌",
+  "subtitle": "追蹤系統中的所有操作記錄",
+  "filters": {
+    "action": "操作類型",
+    "user": "使用者",
+    "entity": "實體類型",
+    "dateRange": "日期範圍",
+    "allActions": "所有操作",
+    "allUsers": "所有使用者",
+    "allEntities": "所有實體"
+  },
+  "actions": {
+    "create": "建立",
+    "update": "更新",
+    "delete": "刪除",
+    "login": "登入",
+    "logout": "登出",
+    "assign": "指派",
+    "unassign": "取消指派",
+    "statusChange": "狀態變更",
+    "comment": "留言",
+    "upload": "上傳",
+    "download": "下載"
+  },
+  "entities": {
+    "task": "任務",
+    "project": "專案",
+    "space": "工作空間",
+    "user": "使用者",
+    "comment": "留言",
+    "attachment": "附件"
+  },
+  "columns": {
+    "timestamp": "時間",
+    "user": "使用者",
+    "action": "操作",
+    "entity": "實體",
+    "details": "詳情",
+    "ipAddress": "IP 位址"
+  },
+  "details": {
+    "before": "變更前",
+    "after": "變更後",
+    "changes": "變更內容"
+  },
+  "export": {
+    "title": "匯出日誌",
+    "csv": "匯出為 CSV",
+    "json": "匯出為 JSON"
+  },
+  "empty": {
+    "title": "沒有稽核記錄",
+    "description": "目前沒有符合條件的稽核記錄"
+  }
+}

frontend/public/locales/zh-TW/auth.json

@@ -0,0 +1,28 @@
+{
+  "login": {
+    "title": "登入",
+    "subtitle": "登入您的帳戶",
+    "email": "電子郵件",
+    "emailPlaceholder": "請輸入電子郵件",
+    "password": "密碼",
+    "passwordPlaceholder": "請輸入密碼",
+    "rememberMe": "記住我",
+    "forgotPassword": "忘記密碼？",
+    "submit": "登入",
+    "loggingIn": "登入中...",
+    "noAccount": "還沒有帳戶？",
+    "signUp": "註冊"
+  },
+  "errors": {
+    "invalidCredentials": "電子郵件或密碼錯誤",
+    "accountLocked": "帳戶已被鎖定，請聯繫管理員",
+    "emailRequired": "請輸入電子郵件",
+    "passwordRequired": "請輸入密碼",
+    "invalidEmail": "請輸入有效的電子郵件地址",
+    "loginFailed": "登入失敗，請稍後再試"
+  },
+  "welcome": {
+    "title": "專案控制中心",
+    "subtitle": "管理您的專案、任務和團隊"
+  }
+}

frontend/public/locales/zh-TW/common.json

@@ -0,0 +1,102 @@
+{
+  "buttons": {
+    "save": "儲存",
+    "cancel": "取消",
+    "delete": "刪除",
+    "edit": "編輯",
+    "create": "建立",
+    "close": "關閉",
+    "confirm": "確認",
+    "back": "返回",
+    "next": "下一步",
+    "previous": "上一步",
+    "submit": "提交",
+    "reset": "重置",
+    "search": "搜尋",
+    "filter": "篩選",
+    "export": "匯出",
+    "import": "匯入",
+    "refresh": "重新整理",
+    "add": "新增",
+    "remove": "移除",
+    "view": "檢視",
+    "download": "下載",
+    "upload": "上傳"
+  },
+  "labels": {
+    "loading": "載入中...",
+    "noData": "暫無資料",
+    "required": "必填",
+    "optional": "選填",
+    "all": "全部",
+    "none": "無",
+    "yes": "是",
+    "no": "否",
+    "active": "啟用",
+    "inactive": "停用",
+    "enabled": "已啟用",
+    "disabled": "已停用",
+    "actions": "操作",
+    "details": "詳情",
+    "description": "描述",
+    "name": "名稱",
+    "title": "標題",
+    "status": "狀態",
+    "type": "類型",
+    "date": "日期",
+    "time": "時間",
+    "createdAt": "建立時間",
+    "updatedAt": "更新時間",
+    "createdBy": "建立者",
+    "assignee": "負責人",
+    "selectAssignee": "選擇負責人...",
+    "searchUsers": "搜尋使用者...",
+    "noUsersFound": "找不到使用者",
+    "typeToSearch": "輸入以搜尋使用者"
+  },
+  "messages": {
+    "success": "操作成功",
+    "error": "操作失敗",
+    "confirmDelete": "確定要刪除嗎？此操作無法復原。",
+    "unsavedChanges": "您有未儲存的變更，確定要離開嗎？",
+    "networkError": "網路連線錯誤，請稍後再試",
+    "sessionExpired": "工作階段已過期，請重新登入",
+    "permissionDenied": "您沒有權限執行此操作",
+    "notFound": "找不到請求的資源"
+  },
+  "validation": {
+    "required": "此欄位為必填",
+    "email": "請輸入有效的電子郵件地址",
+    "minLength": "至少需要 {{min}} 個字元",
+    "maxLength": "最多 {{max}} 個字元",
+    "invalidFormat": "格式不正確"
+  },
+  "nav": {
+    "dashboard": "儀表板",
+    "spaces": "工作空間",
+    "projects": "專案",
+    "tasks": "任務",
+    "workload": "工作負載",
+    "health": "專案健康度",
+    "audit": "稽核日誌",
+    "settings": "設定",
+    "logout": "登出"
+  },
+  "language": {
+    "switch": "切換語言",
+    "zhTW": "繁體中文",
+    "en": "English"
+  },
+  "notifications": {
+    "title": "通知",
+    "markAllRead": "全部標為已讀",
+    "noNotifications": "沒有通知",
+    "viewAll": "查看全部"
+  },
+  "pagination": {
+    "page": "第 {{page}} 頁",
+    "of": "共 {{total}} 頁",
+    "showing": "顯示 {{from}}-{{to}} 筆，共 {{total}} 筆",
+    "itemsPerPage": "每頁顯示"
+  }
+}

frontend/public/locales/zh-TW/dashboard.json

@@ -0,0 +1,47 @@
+{
+  "title": "儀表板",
+  "welcome": "歡迎回來，{{name}}",
+  "stats": {
+    "myTasks": "我的任務",
+    "overdueTasks": "逾期任務",
+    "completedTasks": "已完成任務",
+    "activeProjects": "進行中專案",
+    "teamMembers": "團隊成員",
+    "totalTasks": "總任務數",
+    "pendingReview": "待審核"
+  },
+  "sections": {
+    "recentActivity": "近期活動",
+    "upcomingDeadlines": "即將到期",
+    "myAssignedTasks": "指派給我的任務",
+    "projectOverview": "專案概覽",
+    "quickActions": "快速操作"
+  },
+  "activity": {
+    "taskCreated": "建立了任務「{{task}}」",
+    "taskCompleted": "完成了任務「{{task}}」",
+    "taskAssigned": "將任務「{{task}}」指派給 {{assignee}}",
+    "commentAdded": "在任務「{{task}}」新增了留言",
+    "projectCreated": "建立了專案「{{project}}」",
+    "noRecentActivity": "暫無近期活動"
+  },
+  "deadlines": {
+    "today": "今天到期",
+    "tomorrow": "明天到期",
+    "thisWeek": "本週到期",
+    "overdue": "已逾期",
+    "noUpcoming": "近期沒有待處理的截止日期"
+  },
+  "quickActions": {
+    "createTask": "建立任務",
+    "createProject": "建立專案",
+    "viewAllTasks": "查看所有任務",
+    "viewWorkload": "查看工作負載"
+  },
+  "widgets": {
+    "tasksByStatus": "依狀態分類的任務",
+    "tasksByPriority": "依優先順序分類的任務",
+    "projectProgress": "專案進度",
+    "teamWorkload": "團隊工作負載"
+  }
+}

frontend/public/locales/zh-TW/health.json

@@ -0,0 +1,48 @@
+{
+  "title": "專案健康度",
+  "subtitle": "監控專案的整體健康狀況",
+  "overall": {
+    "title": "整體健康度",
+    "healthy": "健康",
+    "atRisk": "風險中",
+    "critical": "危急"
+  },
+  "metrics": {
+    "schedule": "進度",
+    "budget": "預算",
+    "scope": "範圍",
+    "quality": "品質",
+    "resources": "資源"
+  },
+  "status": {
+    "onTrack": "正常進行",
+    "delayed": "延遲",
+    "ahead": "超前",
+    "overBudget": "超支",
+    "underBudget": "低於預算"
+  },
+  "indicators": {
+    "title": "健康指標",
+    "taskCompletion": "任務完成率",
+    "onTimeDelivery": "準時交付率",
+    "blockedTasks": "阻擋任務數",
+    "overdueRate": "逾期率",
+    "velocityTrend": "速度趨勢"
+  },
+  "risks": {
+    "title": "風險",
+    "high": "高風險",
+    "medium": "中風險",
+    "low": "低風險",
+    "mitigated": "已緩解"
+  },
+  "actions": {
+    "viewDetails": "查看詳情",
+    "exportReport": "匯出報告",
+    "setAlert": "設定警示"
+  },
+  "empty": {
+    "title": "沒有健康度資料",
+    "description": "專案需要更多資料才能顯示健康度指標"
+  }
+}

frontend/public/locales/zh-TW/projects.json

@@ -0,0 +1,50 @@
+{
+  "title": "專案",
+  "createProject": "建立專案",
+  "editProject": "編輯專案",
+  "deleteProject": "刪除專案",
+  "projectSettings": "專案設定",
+  "fields": {
+    "name": "名稱",
+    "namePlaceholder": "輸入專案名稱",
+    "description": "描述",
+    "descriptionPlaceholder": "輸入專案描述",
+    "status": "狀態",
+    "startDate": "開始日期",
+    "endDate": "結束日期",
+    "owner": "專案負責人",
+    "space": "工作空間"
+  },
+  "status": {
+    "planning": "規劃中",
+    "active": "進行中",
+    "on_hold": "暫停",
+    "completed": "已完成",
+    "cancelled": "已取消"
+  },
+  "tabs": {
+    "overview": "概覽",
+    "tasks": "任務",
+    "members": "成員",
+    "settings": "設定",
+    "files": "檔案",
+    "activity": "活動紀錄"
+  },
+  "stats": {
+    "totalTasks": "總任務數",
+    "completedTasks": "已完成",
+    "inProgress": "進行中",
+    "overdue": "逾期",
+    "progress": "整體進度"
+  },
+  "messages": {
+    "created": "專案已建立",
+    "updated": "專案已更新",
+    "deleted": "專案已刪除",
+    "confirmDelete": "確定要刪除此專案嗎？此操作將刪除所有相關任務。"
+  },
+  "empty": {
+    "title": "沒有專案",
+    "description": "建立您的第一個專案來開始管理任務"
+  }
+}

frontend/public/locales/zh-TW/settings.json

@@ -0,0 +1,73 @@
+{
+  "title": "設定",
+  "projectSettings": "專案設定",
+  "tabs": {
+    "general": "一般",
+    "members": "成員",
+    "customFields": "自訂欄位",
+    "notifications": "通知",
+    "integrations": "整合",
+    "danger": "危險區域"
+  },
+  "general": {
+    "title": "一般設定",
+    "projectName": "專案名稱",
+    "description": "描述",
+    "status": "狀態",
+    "visibility": "可見性",
+    "public": "公開",
+    "private": "私人"
+  },
+  "members": {
+    "title": "成員管理",
+    "invite": "邀請成員",
+    "inviteByEmail": "透過電子郵件邀請",
+    "emailPlaceholder": "輸入電子郵件地址",
+    "role": "角色",
+    "changeRole": "變更角色",
+    "remove": "移除成員",
+    "confirmRemove": "確定要移除此成員嗎？"
+  },
+  "customFields": {
+    "title": "自訂欄位",
+    "add": "新增欄位",
+    "edit": "編輯欄位",
+    "delete": "刪除欄位",
+    "fieldName": "欄位名稱",
+    "fieldType": "欄位類型",
+    "required": "必填",
+    "types": {
+      "text": "文字",
+      "number": "數字",
+      "date": "日期",
+      "select": "下拉選單",
+      "multiSelect": "多選",
+      "checkbox": "核取方塊"
+    }
+  },
+  "notifications": {
+    "title": "通知設定",
+    "email": "電子郵件通知",
+    "inApp": "應用內通知",
+    "taskAssigned": "任務指派給我時",
+    "taskCompleted": "任務完成時",
+    "commentAdded": "新增留言時",
+    "dueDateApproaching": "截止日期即將到來時"
+  },
+  "danger": {
+    "title": "危險區域",
+    "archive": "封存專案",
+    "archiveDescription": "封存此專案。封存後專案將變為唯讀。",
+    "delete": "刪除專案",
+    "deleteDescription": "永久刪除此專案及其所有資料。此操作無法復原。",
+    "confirmArchive": "確定要封存此專案嗎？",
+    "confirmDelete": "確定要刪除此專案嗎？請輸入專案名稱以確認：",
+    "typeToConfirm": "輸入「{{name}}」以確認"
+  },
+  "messages": {
+    "saved": "設定已儲存",
+    "memberInvited": "已發送邀請",
+    "memberRemoved": "成員已移除",
+    "roleChanged": "角色已變更"
+  }
+}

frontend/public/locales/zh-TW/spaces.json

@@ -0,0 +1,39 @@
+{
+  "title": "工作空間",
+  "createSpace": "建立工作空間",
+  "editSpace": "編輯工作空間",
+  "deleteSpace": "刪除工作空間",
+  "fields": {
+    "name": "名稱",
+    "namePlaceholder": "輸入工作空間名稱",
+    "description": "描述",
+    "descriptionPlaceholder": "輸入工作空間描述",
+    "icon": "圖示",
+    "color": "顏色"
+  },
+  "members": {
+    "title": "成員",
+    "add": "新增成員",
+    "remove": "移除成員",
+    "role": "角色",
+    "owner": "擁有者",
+    "admin": "管理員",
+    "member": "成員",
+    "viewer": "檢視者"
+  },
+  "stats": {
+    "projects": "專案數",
+    "members": "成員數",
+    "tasks": "任務數"
+  },
+  "messages": {
+    "created": "工作空間已建立",
+    "updated": "工作空間已更新",
+    "deleted": "工作空間已刪除",
+    "confirmDelete": "確定要刪除此工作空間嗎？此操作將刪除所有相關專案和任務。"
+  },
+  "empty": {
+    "title": "沒有工作空間",
+    "description": "建立您的第一個工作空間來組織專案"
+  }
+}

frontend/public/locales/zh-TW/tasks.json

@@ -0,0 +1,134 @@
+{
+  "title": "任務",
+  "createTask": "建立任務",
+  "editTask": "編輯任務",
+  "deleteTask": "刪除任務",
+  "taskDetails": "任務詳情",
+  "fields": {
+    "title": "標題",
+    "titlePlaceholder": "輸入任務標題",
+    "description": "描述",
+    "descriptionPlaceholder": "輸入任務描述",
+    "status": "狀態",
+    "priority": "優先順序",
+    "assignee": "負責人",
+    "dueDate": "截止日期",
+    "startDate": "開始日期",
+    "estimatedHours": "預估工時",
+    "actualHours": "實際工時",
+    "progress": "進度",
+    "tags": "標籤",
+    "parent": "父任務",
+    "subtasks": "子任務",
+    "attachments": "附件",
+    "comments": "留言",
+    "watchers": "關注者",
+    "blockers": "阻擋項目"
+  },
+  "status": {
+    "todo": "待處理",
+    "in_progress": "進行中",
+    "review": "審核中",
+    "done": "已完成",
+    "cancelled": "已取消",
+    "blocked": "被阻擋"
+  },
+  "priority": {
+    "low": "低",
+    "medium": "中",
+    "high": "高",
+    "urgent": "緊急"
+  },
+  "views": {
+    "list": "列表",
+    "kanban": "看板",
+    "calendar": "日曆",
+    "gantt": "甘特圖",
+    "timeline": "時間軸"
+  },
+  "filters": {
+    "all": "全部任務",
+    "myTasks": "我的任務",
+    "unassigned": "未指派",
+    "overdue": "逾期",
+    "dueThisWeek": "本週到期",
+    "highPriority": "高優先順序",
+    "recentlyUpdated": "最近更新"
+  },
+  "sort": {
+    "sortBy": "排序方式",
+    "dueDate": "截止日期",
+    "priority": "優先順序",
+    "status": "狀態",
+    "title": "標題",
+    "createdAt": "建立時間",
+    "updatedAt": "更新時間",
+    "ascending": "升序",
+    "descending": "降序"
+  },
+  "actions": {
+    "assign": "指派",
+    "reassign": "重新指派",
+    "changeStatus": "變更狀態",
+    "changePriority": "變更優先順序",
+    "addSubtask": "新增子任務",
+    "addComment": "新增留言",
+    "addAttachment": "新增附件",
+    "addWatcher": "新增關注者",
+    "removeWatcher": "移除關注者",
+    "duplicate": "複製任務",
+    "archive": "封存",
+    "restore": "還原",
+    "moveToProject": "移至專案"
+  },
+  "subtasks": {
+    "title": "子任務",
+    "add": "新增子任務",
+    "placeholder": "輸入子任務標題",
+    "completed": "已完成 {{count}} / {{total}}",
+    "empty": "沒有子任務"
+  },
+  "comments": {
+    "title": "留言",
+    "add": "新增留言",
+    "placeholder": "輸入您的留言...",
+    "edited": "已編輯",
+    "delete": "刪除留言",
+    "confirmDelete": "確定要刪除此留言嗎？",
+    "empty": "還沒有留言",
+    "reply": "回覆"
+  },
+  "attachments": {
+    "title": "附件",
+    "add": "新增附件",
+    "upload": "上傳檔案",
+    "dragDrop": "拖放檔案至此或點擊上傳",
+    "maxSize": "最大檔案大小：{{size}}MB",
+    "downloading": "下載中...",
+    "empty": "沒有附件"
+  },
+  "blockers": {
+    "title": "阻擋項目",
+    "add": "新增阻擋項目",
+    "blockedBy": "被以下任務阻擋",
+    "blocking": "正在阻擋以下任務",
+    "remove": "移除阻擋關係",
+    "empty": "沒有阻擋項目"
+  },
+  "messages": {
+    "created": "任務已建立",
+    "updated": "任務已更新",
+    "deleted": "任務已刪除",
+    "statusChanged": "狀態已變更為「{{status}}」",
+    "assigned": "已指派給 {{assignee}}",
+    "unassigned": "已取消指派",
+    "commentAdded": "留言已新增",
+    "attachmentUploaded": "附件已上傳",
+    "confirmDelete": "確定要刪除此任務嗎？此操作無法復原。"
+  },
+  "empty": {
+    "title": "沒有任務",
+    "description": "目前沒有任務。建立您的第一個任務開始吧！",
+    "filtered": "沒有符合篩選條件的任務"
+  }
+}

frontend/public/locales/zh-TW/workload.json

@@ -0,0 +1,42 @@
+{
+  "title": "工作負載",
+  "subtitle": "檢視團隊成員的工作負載分佈",
+  "filters": {
+    "project": "專案",
+    "allProjects": "所有專案",
+    "dateRange": "日期範圍",
+    "thisWeek": "本週",
+    "thisMonth": "本月",
+    "custom": "自訂"
+  },
+  "metrics": {
+    "totalHours": "總工時",
+    "assignedTasks": "指派任務數",
+    "completedTasks": "已完成任務",
+    "overdueTasks": "逾期任務",
+    "utilization": "使用率"
+  },
+  "chart": {
+    "hoursPerDay": "每日工時",
+    "taskDistribution": "任務分佈",
+    "byProject": "依專案",
+    "byPriority": "依優先順序"
+  },
+  "team": {
+    "title": "團隊成員",
+    "member": "成員",
+    "allocated": "已分配",
+    "available": "可用",
+    "overloaded": "超載",
+    "underutilized": "低使用率"
+  },
+  "status": {
+    "balanced": "平衡",
+    "overloaded": "超載",
+    "underutilized": "低使用率"
+  },
+  "empty": {
+    "title": "沒有工作負載資料",
+    "description": "目前沒有足夠的資料來顯示工作負載"
+  }
+}