### What problem does this PR solve?
This PR adds missing web API tests (system, search, KB, LLM, plugin,
connector). It also addresses a contract mismatch that was causing test
failures: metadata updates did not persist new keys (update‑only
behavior).
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
- [x] Other (please describe): Test coverage expansion and test helper
instrumentation
### 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)
### What problem does this PR solve?
- Add new test suite for document app with
create/list/parse/upload/remove tests
- Update API URLs to use version variable from config in HTTP and web
API tests
### Type of change
- [x] Add test cases
