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-rate-limiting-expansion/tasks.md

@@ -0,0 +1,30 @@
+# Tasks: Expand Rate Limiting
+
+## 1. Configuration
+- [x] 1.1 Define rate limit tiers in config (standard, sensitive, heavy)
+- [x] 1.2 Standard: 60/minute, Sensitive: 20/minute, Heavy: 5/minute
+- [x] 1.3 Add environment variable overrides for rate limits
+
+## 2. Task API Rate Limiting
+- [x] 2.1 Apply "standard" rate limit to POST /api/tasks
+- [x] 2.2 Apply "standard" rate limit to PATCH /api/tasks/{id}
+- [x] 2.3 Apply "heavy" rate limit to bulk task operations
+
+## 3. Report API Rate Limiting
+- [x] 3.1 Apply "heavy" rate limit to POST /api/reports/generate
+- [x] 3.2 Apply "sensitive" rate limit to report export endpoints
+
+## 4. Other Sensitive Endpoints
+- [x] 4.1 Apply "sensitive" rate limit to password change endpoint (N/A - uses external auth)
+- [x] 4.2 Apply "sensitive" rate limit to attachment upload
+- [x] 4.3 Apply "standard" rate limit to comment creation
+
+## 5. Response Headers
+- [x] 5.1 Include X-RateLimit-Limit header in responses
+- [x] 5.2 Include X-RateLimit-Remaining header
+- [x] 5.3 Include X-RateLimit-Reset header
+
+## 6. Testing
+- [x] 6.1 Test rate limit enforcement
+- [x] 6.2 Test rate limit reset after window
+- [x] 6.3 Verify 429 Too Many Requests response