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/utils/test_preview_selection.py

@@ -12,6 +12,7 @@ def test_select_preview_returns_first_when_blur_disabled():
 
     selected, level = select_preview_media(images, blur_mature_content=False)
 
+    assert selected is not None
     assert selected["url"] == "nsfw"
     assert level == 32
 
@@ -40,6 +41,7 @@ def test_select_preview_respects_configurable_threshold(threshold_name, expected
         mature_threshold=NSFW_LEVELS[threshold_name],
     )
 
+    assert selected is not None
     assert selected["url"] == expected_url
     assert level == next(item["nsfwLevel"] for item in images if item["url"] == expected_url)