feat: implement 5 QA-driven security and quality proposals

Implemented proposals from comprehensive QA review:

1. extend-csrf-protection
   - Add POST to CSRF protected methods in frontend
   - Global CSRF middleware for all state-changing operations
   - Update tests with CSRF token fixtures

2. tighten-cors-websocket-security
   - Replace wildcard CORS with explicit method/header lists
   - Disable query parameter auth in production (code 4002)
   - Add per-user WebSocket connection limit (max 5, code 4005)

3. shorten-jwt-expiry
   - Reduce JWT expiry from 7 days to 60 minutes
   - Add refresh token support with 7-day expiry
   - Implement token rotation on refresh
   - Frontend auto-refresh when token near expiry (<5 min)

4. fix-frontend-quality
   - Add React.lazy() code splitting for all pages
   - Fix useCallback dependency arrays (Dashboard, Comments)
   - Add localStorage data validation in AuthContext
   - Complete i18n for AttachmentUpload component

5. enhance-backend-validation
   - Add SecurityAuditMiddleware for access denied logging
   - Add ErrorSanitizerMiddleware for production error messages
   - Protect /health/detailed with admin authentication
   - Add input length validation (comment 5000, desc 10000)

All 521 backend tests passing. Frontend builds successfully.

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

backend/tests/conftest.py

@@ -166,3 +166,20 @@ def admin_token(client, mock_redis):
     mock_redis.setex("session:00000000-0000-0000-0000-000000000001", 900, token)
 
     return token
+
+
+@pytest.fixture
+def csrf_token():
+    """Generate a CSRF token for the admin user."""
+    from app.core.security import generate_csrf_token
+
+    return generate_csrf_token("00000000-0000-0000-0000-000000000001")
+
+
+@pytest.fixture
+def auth_headers(admin_token, csrf_token):
+    """Get complete auth headers including both Authorization and CSRF token."""
+    return {
+        "Authorization": f"Bearer {admin_token}",
+        "X-CSRF-Token": csrf_token,
+    }