When a track reaches natural EOF (player alive, no stream error), play the
next episode from the source that started it — search results, show, or
Feed — and stop at the end of the list. A crashed/killed daemon or failed
stream never auto-advances.
- add audio-queue.ts: pure next/prev selection from the navigation source
- audio-player: expose getPlaybackError() to distinguish EOF from failure
- useAudio: finalizeTrackEnd(autoAdvance) wiring, re-selecting the current
episode no longer reloads from stale saved progress
- tests: audio-queue units, auto-advance integration (real mpv + local
WAVs over HTTP), backend re-select no-reload test
