- Add `ChapterWithPages` model and `MangaReaderController` (FamilyAsyncNotifier)
to load chapter + pages in a single provider (`mangaReaderProvider`)
- Replace synchronous Isar fetch in `MangaReaderView` with `ref.watch(mangaReaderProvider)`
- Unify loading, error, and data states using a shared `scaffoldWith` helper
- Remove duplicated `Scaffold`/`AppBar` boilerplate and inline SystemChrome restore logic
- Simplify error handling