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>

backend/tests/test_attachments.py

@@ -239,6 +239,8 @@ class TestAttachmentAPI:
 
     def test_delete_attachment(self, client, test_user_token, test_task, db):
         """Test soft deleting an attachment."""
+        from app.core.security import generate_csrf_token
+
         attachment = Attachment(
             id=str(uuid.uuid4()),
             task_id=test_task.id,
@@ -252,9 +254,15 @@ class TestAttachmentAPI:
         db.add(attachment)
         db.commit()
 
+        # Generate CSRF token for the user
+        csrf_token = generate_csrf_token(test_task.created_by)
+
         response = client.delete(
             f"/api/attachments/{attachment.id}",
-            headers={"Authorization": f"Bearer {test_user_token}"},
+            headers={
+                "Authorization": f"Bearer {test_user_token}",
+                "X-CSRF-Token": csrf_token,
+            },
         )
 
         assert response.status_code == 200