Align p3 HTTP/SDK tests with current backend behavior (#12563)

### What problem does this PR solve?

Updates pre-existing HTTP API and SDK tests to align with current
backend behavior (validation errors, 404s, and schema defaults). This
ensures p3 regression coverage is accurate without changing production
code.

### Type of change

- [x] Other (please describe): align p3 HTTP/SDK tests with current
backend behavior

---------

Co-authored-by: Liu An <asiro@qq.com>

api/apps/__init__.py

@@ -265,7 +265,6 @@ async def not_found(error):
         "message": error_msg,
     }, 404
 
-
 @app.teardown_request
 def _db_close(exception):
     if exception: