test(05-06): promote 11 integration test stubs to real passing tests

- test_connect_google_drive: OAuth initiate redirects to Google (Redis mocked)
- test_oauth_callback_valid_state: valid state + mocked Flow.fetch_token → 302 (CLOUD-01)
- test_oauth_callback_invalid_state: invalid state → error redirect (CLOUD-01)
- test_webdav_connect_validates: localhost URL → 422 (D-17 SSRF)
- test_credentials_enc_not_exposed: credentials_enc absent from response (CLOUD-02, SEC-08)
- test_cloud_upload_no_presigned: cloud upload returns no upload_url (CLOUD-03)
- test_connection_status_display: ACTIVE status in list response (CLOUD-04)
- test_invalid_grant_sets_requires_reauth: 503 on invalid_grant (CLOUD-05)
- test_disconnect_deletes_credentials: DELETE 204 + DB row gone (CLOUD-06)
- test_admin_cannot_see_credentials: admin gets 403 (SEC-08 IDOR)
- test_cross_user_idor: wrong-owner delete → 404 (SEC-08 IDOR)

Also fix CloudConnectionOut.id field validator to accept UUID objects from ORM
(Rule 1: Bug - UUID id caused pydantic validation error on list_connections)

All 20 cloud tests PASSED; full suite: 282 passed, 1 pre-existing failure

backend/tests/test_cloud.py

@@ -204,7 +204,6 @@ async def test_connect_google_drive(async_client, db_session, monkeypatch):
 async def test_oauth_callback_valid_state(async_client, db_session, monkeypatch):
     """GET /api/cloud/oauth/callback/google_drive with valid state stores credentials and redirects."""
     from main import app
-    from services.auth import hash_password
 
     # Create a user in DB (callback looks up user from Redis-stored user_id)
     auth = await _create_user_and_token(db_session, role="user")
@@ -215,7 +214,7 @@ async def test_oauth_callback_valid_state(async_client, db_session, monkeypatch)
     fake_redis = FakeRedis(initial={f"oauth_state:{state_token}": user_id.encode()})
     app.state.redis = fake_redis
 
-    # Mock Flow.fetch_token to avoid real OAuth network call
+    # Mock Flow credentials — the callback does asyncio.to_thread(flow.fetch_token, code=code)
     mock_creds = MagicMock()
     mock_creds.token = "ya29.test_access_token"
     mock_creds.refresh_token = "1//test_refresh_token"
@@ -224,15 +223,14 @@ async def test_oauth_callback_valid_state(async_client, db_session, monkeypatch)
     mock_creds.client_secret = "test_client_secret"
     mock_creds.expiry = None
 
-    def fake_fetch_token(code):
-        pass  # no-op — credentials are set below
-
     mock_flow = MagicMock()
     mock_flow.credentials = mock_creds
-    mock_flow.authorization_url.return_value = ("https://accounts.google.com/auth", "state")
-    mock_flow.fetch_token = fake_fetch_token
+    mock_flow.fetch_token = MagicMock(return_value=None)  # sync — called via to_thread
 
-    with patch("api.cloud.Flow") as mock_flow_class:
+    # Flow is imported lazily inside oauth_callback with:
+    #   from google_auth_oauthlib.flow import Flow
+    # We patch the module-level name so the lazy import picks up our mock.
+    with patch("google_auth_oauthlib.flow.Flow") as mock_flow_class:
         mock_flow_class.from_client_config.return_value = mock_flow
 
         resp = await async_client.get(
@@ -360,10 +358,15 @@ async def test_cloud_upload_no_presigned(
         credentials_enc=credentials_enc,
     )
 
-    # Mock GoogleDriveBackend.put_object to avoid real Google Drive call
+    # Mock GoogleDriveBackend.put_object to avoid real Google Drive call.
+    # GoogleDriveBackend is imported lazily inside the endpoint function body, so we
+    # patch at the source module (storage.google_drive_backend) rather than api.documents.
+    # Also mock extract_and_classify.delay to avoid Celery/Redis connection in unit tests.
     mock_put = AsyncMock(return_value="drive_file_id_123")
+    mock_delay = MagicMock()
+    monkeypatch.setattr("api.documents.extract_and_classify.delay", mock_delay)
 
-    with patch("api.documents.GoogleDriveBackend") as mock_gd_class:
+    with patch("storage.google_drive_backend.GoogleDriveBackend") as mock_gd_class:
         mock_instance = MagicMock()
         mock_instance.put_object = mock_put
         mock_gd_class.return_value = mock_instance