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/en/settings.json

@@ -39,13 +39,39 @@
   },
   "members": {
     "title": "Member Management",
+    "description": "Manage users who can access this project. Project members can view and edit project content.",
+    "addMember": "Add Member",
     "invite": "Invite Member",
     "inviteByEmail": "Invite by email",
     "emailPlaceholder": "Enter email address",
+    "selectUser": "Select User",
+    "searchUserPlaceholder": "Search users...",
+    "user": "User",
     "role": "Role",
+    "joinedAt": "Joined",
     "changeRole": "Change Role",
-    "remove": "Remove Member",
-    "confirmRemove": "Are you sure you want to remove this member?"
+    "remove": "Remove",
+    "confirmRemove": "Are you sure you want to remove this member?",
+    "removeConfirmTitle": "Remove Member",
+    "removeConfirmMessage": "Are you sure you want to remove {{name}} from this project? They will no longer have access.",
+    "empty": "No members in this project yet.",
+    "emptyHint": "Click \"Add Member\" to add project members.",
+    "loadError": "Failed to load member list",
+    "addError": "Failed to add member",
+    "removeError": "Failed to remove member",
+    "roleChangeError": "Failed to change role",
+    "memberAdded": "Member added successfully",
+    "adding": "Adding...",
+    "selectUserRequired": "Please select a user to add",
+    "alreadyMember": "This user is already a project member",
+    "roles": {
+      "member": "Member",
+      "admin": "Admin"
+    },
+    "roleHelp": {
+      "member": "Members can view and edit tasks in this project.",
+      "admin": "Admins can manage project settings and members."
+    }
   },
   "customFields": {
     "title": "Custom Fields",
@@ -104,6 +130,12 @@
     },
     "validation": {
       "nameRequired": "Field name is required"
+    },
+    "circularError": {
+      "title": "Circular Reference Detected",
+      "description": "This formula creates a circular reference, which is not allowed.",
+      "cyclePath": "Reference Cycle",
+      "helpText": "To resolve this issue, modify the formula to avoid referencing fields that directly or indirectly reference this field."
     }
   },
   "notifications": {