JS test gaps: api_tokens and feature_flags pages have no tests #514

Tier 3: test coverage

Problem

Module pages compared with JS test files (tests-js/):

api_tokens (#455) is the newest module, and it shipped security-sensitive UI with no JS tests: the one-time token reveal, copy, and revoke.

On the Python side, coverage is weakest in tenants (test-to-source line ratio about 0.54) and permissions (about 0.66). There are no direct unit tests for tenants/shared_props.py or file_storage/upload_guards.py.

Fix

1. Add smoke and interaction tests for the api_tokens pages. Cover especially that the secret is shown once, is never re-rendered after navigation, and that revoke asks for confirmation.
2. Add feature_flags page tests.
3. Cover the background_tasks mutation flows (retry, purge, outbox replay).
4. Add direct tests for tenants/shared_props.py and file_storage/upload_guards.py.