Adds src/api/endpoints/settings.ts (getSettings/updateSettings,
getScrobbling/updateScrobbling) plus AppSettings/ScrobblingConfig types
and a Settings cache tag. Replaces the "coming soon" scaffolds:
- Playback: stream-quality preference (SegmentedControl), server-synced.
- Scrobbling: enable + provider (Last.fm/ListenBrainz) + username +
write-only session key, with a linked/not-linked badge and save states.
Built with modern-sk (Window/SegmentedControl/TextField/Button/Callout/
Badge) + the shared Loading/Error states; en + ru strings added. Server
state flows through RTK Query hooks only (no fetch in components).
Also drops a pre-existing unused TextField import in LibraryPage that was
failing `tsc --noEmit`.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Цвылев Александр Вадимович
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