feat: implement security, error resilience, and query optimization proposals

Security Validation (enhance-security-validation):
- JWT secret validation with entropy checking and pattern detection
- CSRF protection middleware with token generation/validation
- Frontend CSRF token auto-injection for DELETE/PUT/PATCH requests
- MIME type validation with magic bytes detection for file uploads

Error Resilience (add-error-resilience):
- React ErrorBoundary component with fallback UI and retry functionality
- ErrorBoundaryWithI18n wrapper for internationalization support
- Page-level and section-level error boundaries in App.tsx

Query Performance (optimize-query-performance):
- Query monitoring utility with threshold warnings
- N+1 query fixes using joinedload/selectinload
- Optimized project members, tasks, and subtasks endpoints

Bug Fixes:
- WebSocket session management (P0): Return primitives instead of ORM objects
- LIKE query injection (P1): Escape special characters in search queries

Tests: 543 backend tests, 56 frontend tests passing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2026-01-11-add-error-resilience/tasks.md

@@ -0,0 +1,14 @@
+## 1. Error Boundary Implementation
+- [x] 1.1 Create base ErrorBoundary component with fallback UI
+- [x] 1.2 Add error logging/reporting to ErrorBoundary
+- [x] 1.3 Create user-friendly error fallback designs
+
+## 2. Application Integration
+- [x] 2.1 Wrap main App routes with top-level Error Boundary
+- [x] 2.2 Add section-level boundaries around Dashboard, Tasks, Projects
+- [x] 2.3 Add component-level boundaries for complex widgets
+
+## 3. Testing
+- [x] 3.1 Write tests for ErrorBoundary component
+- [x] 3.2 Add integration tests that verify graceful degradation
+- [x] 3.3 Test error recovery flow