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/test_attachments.py

@@ -42,6 +42,22 @@ def test_user_token(client, mock_redis, test_user):
     return token
 
 
+@pytest.fixture
+def test_user_csrf_token(test_user):
+    """Generate a CSRF token for the test user."""
+    from app.core.security import generate_csrf_token
+    return generate_csrf_token(test_user.id)
+
+
+@pytest.fixture
+def test_user_auth_headers(test_user_token, test_user_csrf_token):
+    """Get complete auth headers for test user."""
+    return {
+        "Authorization": f"Bearer {test_user_token}",
+        "X-CSRF-Token": test_user_csrf_token,
+    }
+
+
 @pytest.fixture
 def test_space(db, test_user):
     """Create a test space."""
@@ -154,7 +170,7 @@ class TestFileStorageService:
 class TestAttachmentAPI:
     """Tests for Attachment API endpoints."""
 
-    def test_upload_attachment(self, client, test_user_token, test_task, db, monkeypatch, temp_upload_dir):
+    def test_upload_attachment(self, client, test_user_auth_headers, test_task, db, monkeypatch, temp_upload_dir):
         """Test uploading an attachment."""
         monkeypatch.setattr("app.core.config.settings.UPLOAD_DIR", temp_upload_dir)
 
@@ -163,7 +179,7 @@ class TestAttachmentAPI:
 
         response = client.post(
             f"/api/tasks/{test_task.id}/attachments",
-            headers={"Authorization": f"Bearer {test_user_token}"},
+            headers=test_user_auth_headers,
             files=files,
         )
 
@@ -271,14 +287,14 @@ class TestAttachmentAPI:
         db.refresh(attachment)
         assert attachment.is_deleted == True
 
-    def test_upload_blocked_file_type(self, client, test_user_token, test_task):
+    def test_upload_blocked_file_type(self, client, test_user_auth_headers, test_task):
         """Test that blocked file types are rejected."""
         content = b"malicious content"
         files = {"file": ("virus.exe", BytesIO(content), "application/octet-stream")}
 
         response = client.post(
             f"/api/tasks/{test_task.id}/attachments",
-            headers={"Authorization": f"Bearer {test_user_token}"},
+            headers=test_user_auth_headers,
             files=files,
         )
 
@@ -322,7 +338,7 @@ class TestAttachmentAPI:
         assert data["total"] == 2
         assert len(data["versions"]) == 2
 
-    def test_restore_version(self, client, test_user_token, test_task, db):
+    def test_restore_version(self, client, test_user_auth_headers, test_task, db):
         """Test restoring to a previous version."""
         attachment = Attachment(
             id=str(uuid.uuid4()),
@@ -351,7 +367,7 @@ class TestAttachmentAPI:
 
         response = client.post(
             f"/api/attachments/{attachment.id}/restore/1",
-            headers={"Authorization": f"Bearer {test_user_token}"},
+            headers=test_user_auth_headers,
         )
 
         assert response.status_code == 200