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/services/test_llm_service.py

@@ -57,6 +57,9 @@ class MockSession:
     def __init__(self, response):
         self._response = response
         self.closed = False
+        self.last_url = None
+        self.last_json = None
+        self.last_headers = None
 
     def post(self, url, json=None, headers=None):
         self.last_url = url