Fix : Web API tests by normalizing errors, validation, and uploads (#12620)

### What problem does this PR solve?

Fixes web API behavior mismatches that caused test failures by
normalizing error responses, tightening validations, correcting error
messages, and closing upload file handles.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

test/testcases/test_web_api/conftest.py

@@ -14,7 +14,8 @@
 #  limitations under the License.
 #
 from time import sleep
-
+from ragflow_sdk import RAGFlow
+from configs import HOST_ADDRESS, VERSION
 import pytest
 from common import (
     batch_add_chunks,
@@ -81,7 +82,9 @@ def generate_test_files(request: FixtureRequest, tmp_path):
 def ragflow_tmp_dir(request, tmp_path_factory):
     class_name = request.cls.__name__
     return tmp_path_factory.mktemp(class_name)
-
+@pytest.fixture(scope="session")
+def client(token: str) -> RAGFlow:
+    return RAGFlow(api_key=token, base_url=HOST_ADDRESS, version=VERSION)
 
 @pytest.fixture(scope="session")
 def WebApiAuth(auth):