fix(types): resolve pre-existing basedpyright errors in tests

Fix ~790 basedpyright errors across the test suite:
- Type stub subclasses of real production classes with super().__init__()
- Add missing generic type arguments and Dict[str, Any] annotations
- Add None guards before subscript/member access
- Adapt tests to production API changes (removed dead handlers,
  PersistentModelCache.get_default, _i18n_filter_added location)

tests/metadata_ops/test_readme_processor.py

@@ -19,6 +19,8 @@ _MODULE_PATH = Path(__file__).parents[2] / "py" / "services" / "agent" / "skills
 def R():
     """Load the ``readme_processor`` module once per session."""
     spec = importlib.util.spec_from_file_location("readme_processor", str(_MODULE_PATH))
+    assert spec is not None
+    assert spec.loader is not None
     mod = importlib.util.module_from_spec(spec)
     spec.loader.exec_module(mod)
     return mod