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-permission-enhancements/specs/resource-management/spec.md

@@ -0,0 +1,31 @@
+## ADDED Requirements
+
+### Requirement: Manager Workload Visibility
+The system SHALL allow department managers to view workload data for all members within their department.
+
+#### Scenario: Manager views department member workload
+- **WHEN** a department manager requests workload data for a user in their department
+- **THEN** system returns the workload data for that user
+
+#### Scenario: Manager denied access to other department workload
+- **WHEN** a department manager requests workload data for a user in a different department
+- **THEN** system returns 403 Forbidden error
+
+#### Scenario: Regular user cannot view others' workload
+- **WHEN** a non-manager user requests workload data for another user
+- **THEN** system returns 403 Forbidden error
+
+### Requirement: Cross-Department Project Membership
+The system SHALL support explicit project membership to enable cross-department collaboration.
+
+#### Scenario: Add cross-department member to project
+- **WHEN** project owner adds a user from another department as project member
+- **THEN** user gains access to the project regardless of department
+
+#### Scenario: Project member accesses cross-department project
+- **WHEN** a project member from another department accesses project resources
+- **THEN** system grants access based on project membership
+
+#### Scenario: Non-member denied access despite same department
+- **WHEN** a user not in project membership list attempts to access confidential project
+- **THEN** system denies access unless user is in the project's department