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>

openspec/changes/archive/2026-01-10-add-cycle-detection/tasks.md

@@ -0,0 +1,23 @@
+# Tasks: Add Cycle Detection
+
+## 1. Task Dependency Cycle Detection
+- [x] 1.1 Implement DFS-based cycle detection algorithm in dependency_service.py
+- [x] 1.2 Add validation hook when creating/updating task dependencies
+- [x] 1.3 Return 400 Bad Request with cycle path details when detected
+- [x] 1.4 Add cycle detection check in bulk dependency operations
+
+## 2. Formula Field Cycle Detection
+- [x] 2.1 Parse formula field references to build dependency graph
+- [x] 2.2 Implement cycle detection for formula field references
+- [x] 2.3 Add validation when saving custom field formulas
+- [x] 2.4 Return descriptive error showing the cycle path
+
+## 3. Frontend Feedback
+- [x] 3.1 Display user-friendly error message when cycle detected
+- [x] 3.2 Optionally highlight the problematic dependencies in UI
+
+## 4. Testing
+- [x] 4.1 Add unit tests for cycle detection algorithm
+- [x] 4.2 Test direct circular dependency (A -> B -> A)
+- [x] 4.3 Test indirect circular dependency (A -> B -> C -> A)
+- [x] 4.4 Test formula field circular references