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/proposal.md

@@ -0,0 +1,19 @@
+# Change: Add Frontend Error Resilience
+
+## Why
+
+QA review identified that the frontend lacks React Error Boundaries. When a render error occurs in any component, the entire application crashes with a white screen, providing no recovery path for users.
+
+## What Changes
+
+- Add React Error Boundary components around major application sections
+- Implement graceful degradation with user-friendly error messages
+- Add error reporting mechanism to capture frontend crashes
+
+## Impact
+
+- Affected specs: `dashboard`
+- Affected code:
+  - `frontend/src/components/ErrorBoundary.tsx` - New component
+  - `frontend/src/App.tsx` - Wrap routes with Error Boundaries
+  - `frontend/src/pages/` - Section-level boundaries