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-frontend-improvements/specs/dashboard/spec.md

@@ -0,0 +1,39 @@
+## ADDED Requirements
+
+### Requirement: Responsive Layout
+The system SHALL provide a responsive user interface that adapts to different screen sizes for optimal usability.
+
+#### Scenario: Mobile sidebar behavior
+- **WHEN** user accesses application on mobile device (width < 768px)
+- **THEN** sidebar is hidden by default
+- **THEN** hamburger menu button is visible in header
+- **WHEN** user taps hamburger menu
+- **THEN** sidebar slides in from left with backdrop overlay
+
+#### Scenario: Table responsive behavior
+- **WHEN** user views task list on small screen
+- **THEN** table displays with horizontal scroll or switches to card layout
+- **THEN** all essential information remains accessible
+
+#### Scenario: Touch-friendly interactions
+- **WHEN** user interacts with application on touch device
+- **THEN** all interactive elements have minimum 44x44 pixel tap targets
+- **THEN** sufficient spacing prevents accidental taps
+
+### Requirement: Complete Internationalization
+The system SHALL support complete internationalization with no hardcoded text strings.
+
+#### Scenario: Language switching
+- **WHEN** user changes language preference
+- **THEN** all UI text updates to selected language
+- **THEN** no untranslated strings remain visible
+
+#### Scenario: Date and time localization
+- **WHEN** dates and times are displayed
+- **THEN** format follows user's locale preference
+- **THEN** relative times (e.g., "2 hours ago") are properly translated
+
+#### Scenario: New component text
+- **WHEN** new UI components are added
+- **THEN** all text strings use i18n translation keys
+- **THEN** translations exist for all supported locales