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/routes/test_stats_routes.py

@@ -341,7 +341,7 @@ async def test_handle_stats_page_renders_template(stats_routes):
     assert response.status == 200
     assert response.text == "rendered"
     assert stats_routes.server_i18n.locale_calls[-1] == "ja"
-    assert stats_routes.routes.template_env._i18n_filter_added is True
+    assert stats_routes.routes._i18n_filter_added is True
     assert "t" in stats_routes.routes.template_env.filters
     assert stats_routes.routes.template_env.filters["t"]("greeting") == "translated:greeting"
     assert template_context["is_initializing"] is False