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>

backend/app/schemas/task_dependency.py

@@ -76,3 +76,46 @@ class DependencyValidationError(BaseModel):
     error_type: str  # 'circular', 'self_reference', 'duplicate', 'cross_project'
     message: str
     details: Optional[dict] = None
+
+
+class BulkDependencyItem(BaseModel):
+    """Single dependency item for bulk operations."""
+    predecessor_id: str
+    successor_id: str
+    dependency_type: DependencyType = DependencyType.FS
+    lag_days: int = 0
+
+    @field_validator('lag_days')
+    @classmethod
+    def validate_lag_days(cls, v):
+        if v < -365 or v > 365:
+            raise ValueError('lag_days must be between -365 and 365')
+        return v
+
+
+class BulkDependencyCreate(BaseModel):
+    """Schema for creating multiple dependencies at once."""
+    dependencies: List[BulkDependencyItem]
+
+    @field_validator('dependencies')
+    @classmethod
+    def validate_dependencies(cls, v):
+        if not v:
+            raise ValueError('At least one dependency is required')
+        if len(v) > 50:
+            raise ValueError('Cannot create more than 50 dependencies at once')
+        return v
+
+
+class BulkDependencyValidationResult(BaseModel):
+    """Result of bulk dependency validation."""
+    valid: bool
+    errors: List[dict] = []
+
+
+class BulkDependencyCreateResponse(BaseModel):
+    """Response for bulk dependency creation."""
+    created: List[TaskDependencyResponse]
+    failed: List[dict] = []
+    total_created: int
+    total_failed: int