fix(types): resolve mypy errors in CI

- Add type annotations to flash_middleware in main.py
- Add type: ignore comment for get_flash_messages return type

Fixes CI type check failures in:
- app/main.py:79
- app/presentation/web/flash.py:164

app/presentation/web/flash.py

@@ -161,7 +161,7 @@ def get_flash_messages(request: Request) -> list[dict[str, str]]:
         List of flash message dictionaries.
     """
     if hasattr(request.state, "flash_manager"):
-        return request.state.flash_manager.get_messages()
+        return request.state.flash_manager.get_messages()  # type: ignore[no-any-return]
     return []