feat(audio): bit-perfect hi-res playback + underrun hardening (opt-in alpha)

Safe mode (default): all audio outputs at 44.1 kHz, rodio resamples
internally. Maximum stability out of the box.

Hi-Res mode (alpha toggle): stream opens at the file's native sample rate
(e.g. 88.2/96/192 kHz) for bit-perfect output.

Rust (audio.rs):
- open_stream_for_rate(): CPAL queries device supported configs, finds
  exact rate match or falls back to highest available / device default.
- create_engine() thread: ThreadPriority::Max (silently ignored without
  CAP_SYS_NICE), loop handles rate-switch requests, PIPEWIRE_LATENCY
  scales with rate (8192 frames for >48 kHz ≈ 93 ms quantum), keeps
  PULSE_LATENCY_MSEC in sync.
- audio_play(): hi_res_enabled param gates effective_rate (44100 vs
  native); stream re-opens only when needed; 150 ms PipeWire settle +
  500 ms sink pre-fill (pause→append→sleep→play) for hi-res tracks.
- audio_chain_preload(): hi_res_enabled param; rate-mismatch bail skipped
  in safe mode so gapless chains always work at 44.1 kHz.
- SizedDecoder MSS buffer: 4 MB (was 512 KB) to reduce Symphonia read
  overhead on high-bitrate hi-res files.
- thread-priority crate added to Cargo.toml.

Frontend:
- authStore: enableHiRes (bool, default false) + setEnableHiRes.
- playerStore: hiResEnabled passed to all audio_play /
  audio_chain_preload invoke calls.
- Settings → Audio tab: "Native Hi-Res Playback" toggle with Alpha
  badge and stability warning, i18n for all 7 languages.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/nl.ts

@@ -430,6 +430,9 @@ export const nlTranslation = {
     hotCacheDebounceImmediate: 'Direct',
     hotCacheDebounceSeconds: '{{n}} s',
     hotCacheClearBtn: 'Warme cache wissen',
+    hiResTitle: 'Natieve hi-res-weergave',
+    hiResEnabled: 'Natieve hi-res-weergave inschakelen',
+    hiResDesc: "Beperkt de uitvoer standaard tot 44,1 kHz voor maximale stabiliteit. Alleen inschakelen als hardware en netwerk hoge samplerates (88,2 kHz+) ondersteunen.",
     showArtistImages: 'Artiestafbeeldingen weergeven',
     showArtistImagesDesc: 'Laadt en toont artiestafbeeldingen in het artiestenoverzicht. Standaard uitgeschakeld om server-I/O en netwerkbelasting bij grote bibliotheken te beperken.',
     showTrayIcon: 'Tray-pictogram weergeven',