feat: implement 8 OpenSpec proposals for security, reliability, and UX improvements

## Security Enhancements (P0)
- Add input validation with max_length and numeric range constraints
- Implement WebSocket token authentication via first message
- Add path traversal prevention in file storage service

## Permission Enhancements (P0)
- Add project member management for cross-department access
- Implement is_department_manager flag for workload visibility

## Cycle Detection (P0)
- Add DFS-based cycle detection for task dependencies
- Add formula field circular reference detection
- Display user-friendly cycle path visualization

## Concurrency & Reliability (P1)
- Implement optimistic locking with version field (409 Conflict on mismatch)
- Add trigger retry mechanism with exponential backoff (1s, 2s, 4s)
- Implement cascade restore for soft-deleted tasks

## Rate Limiting (P1)
- Add tiered rate limits: standard (60/min), sensitive (20/min), heavy (5/min)
- Apply rate limits to tasks, reports, attachments, and comments

## Frontend Improvements (P1)
- Add responsive sidebar with hamburger menu for mobile
- Improve touch-friendly UI with proper tap target sizes
- Complete i18n translations for all components

## Backend Reliability (P2)
- Configure database connection pool (size=10, overflow=20)
- Add Redis fallback mechanism with message queue
- Add blocker check before task deletion

## API Enhancements (P3)
- Add standardized response wrapper utility
- Add /health/ready and /health/live endpoints
- Implement project templates with status/field copying

## Tests Added
- test_input_validation.py - Schema and path traversal tests
- test_concurrency_reliability.py - Optimistic locking and retry tests
- test_backend_reliability.py - Connection pool and Redis tests
- test_api_enhancements.py - Health check and template tests

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

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

@@ -39,13 +39,39 @@
   },
   "members": {
     "title": "成員管理",
+    "description": "管理可以存取此專案的使用者。專案成員可以檢視和編輯專案內容。",
+    "addMember": "新增成員",
     "invite": "邀請成員",
     "inviteByEmail": "透過電子郵件邀請",
     "emailPlaceholder": "輸入電子郵件地址",
+    "selectUser": "選擇使用者",
+    "searchUserPlaceholder": "搜尋使用者...",
+    "user": "使用者",
     "role": "角色",
+    "joinedAt": "加入時間",
     "changeRole": "變更角色",
-    "remove": "移除成員",
-    "confirmRemove": "確定要移除此成員嗎？"
+    "remove": "移除",
+    "confirmRemove": "確定要移除此成員嗎？",
+    "removeConfirmTitle": "移除成員",
+    "removeConfirmMessage": "確定要將 {{name}} 從此專案移除嗎？移除後該成員將無法存取此專案。",
+    "empty": "此專案尚無成員。",
+    "emptyHint": "點擊「新增成員」來添加專案成員。",
+    "loadError": "載入成員列表失敗",
+    "addError": "新增成員失敗",
+    "removeError": "移除成員失敗",
+    "roleChangeError": "變更角色失敗",
+    "memberAdded": "成員已新增",
+    "adding": "新增中...",
+    "selectUserRequired": "請選擇要新增的使用者",
+    "alreadyMember": "此使用者已經是專案成員",
+    "roles": {
+      "member": "成員",
+      "admin": "管理員"
+    },
+    "roleHelp": {
+      "member": "成員可以檢視和編輯專案中的任務。",
+      "admin": "管理員可以管理專案設定和成員。"
+    }
   },
   "customFields": {
     "title": "自訂欄位",
@@ -104,6 +130,12 @@
     },
     "validation": {
       "nameRequired": "欄位名稱為必填"
+    },
+    "circularError": {
+      "title": "偵測到循環參照",
+      "description": "此公式會產生循環參照，這是不被允許的。",
+      "cyclePath": "參照循環路徑",
+      "helpText": "要解決此問題，請修改公式以避免參照直接或間接參照此欄位的其他欄位。"
     }
   },
   "notifications": {