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-api-enhancements/specs/dashboard/spec.md

@@ -0,0 +1,57 @@
+## ADDED Requirements
+
+### Requirement: Standardized API Response Format
+The system SHALL return all API responses in a consistent standardized format.
+
+#### Scenario: Successful API response
+- **WHEN** API request succeeds
+- **THEN** response includes success=true
+- **THEN** response includes data field with result
+- **THEN** response includes timestamp field
+
+#### Scenario: Error API response
+- **WHEN** API request fails
+- **THEN** response includes success=false
+- **THEN** response includes error_code field
+- **THEN** response includes message field with description
+
+### Requirement: API Versioning
+The system SHALL support API versioning to enable backwards compatibility during upgrades.
+
+#### Scenario: Versioned API endpoint
+- **WHEN** client calls /api/v1/tasks
+- **THEN** system routes to current version implementation
+- **THEN** response works with v1 client expectations
+
+#### Scenario: Legacy API route
+- **WHEN** client calls /api/tasks (unversioned)
+- **THEN** system routes to default version
+- **THEN** response includes deprecation warning header
+
+### Requirement: Comprehensive Health Check
+The system SHALL provide detailed health check endpoints for monitoring.
+
+#### Scenario: All systems healthy
+- **WHEN** health check is called and all dependencies are available
+- **THEN** response includes status=healthy
+- **THEN** response includes checks object with database=ok, redis=ok
+
+#### Scenario: Partial system failure
+- **WHEN** health check is called and Redis is unavailable
+- **THEN** response includes status=degraded
+- **THEN** response includes checks object with database=ok, redis=error
+
+### Requirement: Project Templates
+The system SHALL support project templates to standardize project creation.
+
+#### Scenario: Create project from template
+- **WHEN** user creates project selecting a template
+- **THEN** system copies TaskStatus definitions from template
+- **THEN** system copies CustomField definitions from template
+- **THEN** project is created with predefined structure
+
+#### Scenario: Save project as template
+- **WHEN** user saves existing project as template
+- **THEN** system creates template with project's TaskStatus definitions
+- **THEN** system creates template with project's CustomField definitions
+- **THEN** template is available for future project creation