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_update_routes.py

@@ -24,7 +24,7 @@ def _fake_request(body=None, query_params=None):
     async def _json():
         return body or {}
 
-    req.json = _json
+    req.json = _json  # pyright: ignore[reportAttributeAccessIssue]
     return req
 
 
@@ -131,7 +131,7 @@ async def test_perform_git_update_preserves_user_dirs(monkeypatch, tmp_path):
     class FakeHeads:
         def __getitem__(self, name):
             class Head:
-                def checkout(self_inner):
+                def checkout(self):
                     calls.append(("head-checkout", (name,)))
             return Head()