Convert AudiobookRow and SeriesRow from FutureBuilder to setState-based
dual-loading pattern (matching AlbumRow). Add caching support for
audiobooks and series to enable instant display and offline fallback.
Root cause: FutureBuilder pattern created Future once in initState.
When connection restored, widget State was preserved via KeepAlive,
_hasLoaded remained true, preventing data re-fetch.
Changes:
- AudiobookRow: setState pattern + getCachedAudiobooks callback
- SeriesRow: setState pattern + getCachedSeries callback
- CacheService: Add audiobook/series caching methods
- Provider: Add *WithCache() and getCached*() methods
- NewHomeScreen: Pass cache callbacks to audiobook/series rows
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
