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>

frontend/public/locales/en/common.json

@@ -112,5 +112,22 @@
     "of": "of {{total}}",
     "showing": "Showing {{from}}-{{to}} of {{total}}",
     "itemsPerPage": "Items per page"
+  },
+  "errorBoundary": {
+    "retry": "Try Again",
+    "page": {
+      "title": "Something went wrong",
+      "message": "We apologize for the inconvenience. Please try refreshing the page or contact support if the problem persists."
+    },
+    "section": {
+      "title": "Unable to load this section",
+      "message": "This section encountered an error. Other parts of the page may still work.",
+      "messageWithName": "{{section}} encountered an error. Other parts of the page may still work."
+    },
+    "widget": {
+      "title": "Widget error",
+      "message": "Unable to display this widget.",
+      "errorSuffix": "error"
+    }
   }
 }