fix(gtea): ruff format + check all gtea files and bridge.py

Clears cc-ci self-test lint failures:
- ruff format: 9 files reformatted (all gtea test files + test_discovery.py)
- ruff check --fix: bridge.py UP017 (datetime.UTC alias) + 6 gtea check errors
- manifest.py B007: rename unused loop variable path → _path (no auto-fix available)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/gitea/test_backup.py

@@ -22,6 +22,6 @@ def test_backup_captures_marker_repo(live_app, meta):
     # backupbot cycles the gitea container during backup — wait for it to be back up.
     generic.assert_serving(live_app, meta)
     user, password = admin_creds(live_app)
-    assert marker_repo_exists(live_app, user, password), (
-        f"{live_app}: ci-marker repo is not present at backup time (backup would capture empty state)"
-    )
+    assert marker_repo_exists(
+        live_app, user, password
+    ), f"{live_app}: ci-marker repo is not present at backup time (backup would capture empty state)"