feat: complete i18n translation for remaining components

- Translate pages: Projects, ProjectHealthPage, ProjectSettings
- Translate components: TaskDetailModal, KanbanBoard, Comments,
  SubtaskList, CalendarView, BlockerDialog
- Add translation keys for tasks namespace: kanban, calendar,
  subtasks.error, comments.error, blockers (full translation)
- Add common.labels.task translation key
- Fix task creation: use original_estimate instead of time_estimate

Translation coverage:
- 10 locale files updated (zh-TW & en)
- 6 page/component files translated
- ~100 new translation keys added

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

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

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

@@ -4,16 +4,26 @@
   "editProject": "編輯專案",
   "deleteProject": "刪除專案",
   "projectSettings": "專案設定",
+  "newProject": "新增專案",
   "fields": {
     "name": "名稱",
     "namePlaceholder": "輸入專案名稱",
+    "title": "專案標題",
+    "titlePlaceholder": "輸入專案標題",
     "description": "描述",
-    "descriptionPlaceholder": "輸入專案描述",
+    "descriptionPlaceholder": "輸入專案描述（選填）",
     "status": "狀態",
     "startDate": "開始日期",
     "endDate": "結束日期",
     "owner": "專案負責人",
-    "space": "工作空間"
+    "space": "工作空間",
+    "securityLevel": "安全等級"
+  },
+  "securityLevel": {
+    "label": "安全等級",
+    "public": "公開 - 所有使用者",
+    "department": "部門 - 僅同部門",
+    "confidential": "機密 - 僅負責人"
   },
   "status": {
     "planning": "規劃中",
@@ -37,10 +47,18 @@
     "overdue": "逾期",
     "progress": "整體進度"
   },
+  "card": {
+    "tasks": "{{count}} 個任務",
+    "owner": "負責人",
+    "noDescription": "沒有描述",
+    "unknown": "未知"
+  },
   "messages": {
     "created": "專案已建立",
     "updated": "專案已更新",
     "deleted": "專案已刪除",
+    "loadFailed": "載入專案失敗",
+    "createFailed": "建立專案失敗",
     "confirmDelete": "確定要刪除此專案嗎？此操作將刪除所有相關任務。"
   },
   "empty": {