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/proposal.md

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+# Change: Add Frontend Responsive Design and i18n Completion
+
+## Why
+The current frontend has usability issues on mobile and tablet devices - sidebar doesn't collapse properly, tables overflow, and some UI elements are not touch-friendly. Additionally, internationalization (i18n) is incomplete with some hardcoded Chinese text remaining in components.
+
+## What Changes
+- Implement responsive sidebar with collapsible behavior on small screens
+- Add responsive table handling with horizontal scroll or card view
+- Complete i18n translation coverage for all UI text
+- Improve touch targets for mobile usability
+
+## Impact
+- Affected specs: dashboard
+- Affected code:
+  - `frontend/src/components/Layout.tsx` - Responsive sidebar
+  - `frontend/src/components/*.tsx` - Responsive styles
+  - `frontend/src/i18n/locales/*.json` - Translation files
+  - `frontend/src/pages/*.tsx` - Replace hardcoded text

openspec/changes/archive/2026-01-10-add-frontend-improvements/specs/dashboard/spec.md

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+## 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

openspec/changes/archive/2026-01-10-add-frontend-improvements/tasks.md

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+# Tasks: Add Frontend Improvements
+
+## 1. Responsive Sidebar
+- [x] 1.1 Add hamburger menu button for mobile screens
+- [x] 1.2 Implement slide-out sidebar behavior on small screens
+- [x] 1.3 Add overlay backdrop when sidebar is open on mobile
+- [x] 1.4 Persist sidebar state preference in local storage
+
+## 2. Responsive Tables
+- [x] 2.1 Add horizontal scroll wrapper for wide tables
+- [x] 2.2 Implement card view alternative for task lists on mobile
+- [x] 2.3 Make table columns prioritized (hide less important on small screens)
+- [x] 2.4 Ensure touch-friendly row actions
+
+## 3. Touch-Friendly UI
+- [x] 3.1 Increase tap target sizes to minimum 44x44 pixels
+- [x] 3.2 Add proper spacing between interactive elements
+- [x] 3.3 Improve drag-and-drop for touch devices on Kanban
+
+## 4. i18n Completion
+- [x] 4.1 Audit all components for hardcoded Chinese text
+- [x] 4.2 Extract remaining strings to translation files
+- [x] 4.3 Add missing translations for en and zh-TW locales
+- [x] 4.4 Ensure date/time formatting uses locale settings
+
+## 5. Testing
+- [x] 5.1 Test on mobile viewport (375px width)
+- [x] 5.2 Test on tablet viewport (768px width)
+- [x] 5.3 Test language switching functionality
+- [x] 5.4 Verify all text is properly translated