fix: Add original_filename param to batch upload test mock

The fake_store function in TestLibreChatUploadBatch had a fixed
parameter list missing the new original_filename kwarg, causing
a TypeError when the endpoint passed it through.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: usnavy13

tests/integration/test_librechat_compat.py

@@ -1901,7 +1901,13 @@ def setup_mocks(self):
         stored_filenames = []
 
         async def fake_store(
-            session_id, filename, content, content_type, is_agent_file, is_read_only=False
+            session_id,
+            filename,
+            content,
+            content_type,
+            is_agent_file,
+            is_read_only=False,
+            original_filename=None,
         ):
             stored_filenames.append(filename)
             return f"fid-{len(stored_filenames)}"