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/proposal.md

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+# Change: Expand Rate Limiting to Sensitive API Endpoints
+
+## Why
+Currently only the login endpoint has rate limiting. Other sensitive operations (task creation, report generation, bulk operations) can be abused through excessive requests, potentially causing service degradation or enabling brute-force attacks.
+
+## What Changes
+- Apply rate limiting to task creation/update endpoints
+- Apply rate limiting to report generation endpoints
+- Apply rate limiting to bulk operation endpoints
+- Add configurable rate limit tiers based on endpoint sensitivity
+
+## Impact
+- Affected specs: user-auth
+- Affected code:
+  - `backend/app/api/tasks/router.py` - Task rate limits
+  - `backend/app/api/reports/router.py` - Report rate limits
+  - `backend/app/core/config.py` - Rate limit configuration

openspec/changes/archive/2026-01-10-add-rate-limiting-expansion/specs/user-auth/spec.md

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+## ADDED Requirements
+
+### Requirement: Comprehensive API Rate Limiting
+The system SHALL enforce rate limits on all sensitive API endpoints to prevent abuse and ensure service availability.
+
+#### Scenario: Task creation rate limit exceeded
+- **WHEN** user exceeds 60 task creation requests per minute
+- **THEN** system returns 429 Too Many Requests
+- **THEN** response includes Retry-After header
+
+#### Scenario: Report generation rate limit exceeded
+- **WHEN** user exceeds 5 report generation requests per minute
+- **THEN** system returns 429 Too Many Requests
+- **THEN** response includes rate limit headers
+
+#### Scenario: Rate limit headers provided
+- **WHEN** user makes any rate-limited API request
+- **THEN** response includes X-RateLimit-Limit header
+- **THEN** response includes X-RateLimit-Remaining header
+- **THEN** response includes X-RateLimit-Reset header
+
+#### Scenario: Rate limit window reset
+- **WHEN** rate limit window expires
+- **THEN** user can make requests again up to the limit
+- **THEN** X-RateLimit-Remaining resets to maximum

openspec/changes/archive/2026-01-10-add-rate-limiting-expansion/tasks.md

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+# 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