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/zh.ts

@@ -426,6 +426,9 @@ export const zhTranslation = {
     hotCacheDebounceImmediate: '立即',
     hotCacheDebounceSeconds: '{{n}} 秒',
     hotCacheClearBtn: '清空热缓存',
+    hiResTitle: '原生高清晰度播放',
+    hiResEnabled: '启用原生高清晰度播放',
+    hiResDesc: "默认强制 44.1 kHz 输出以获得最大稳定性。仅在硬件和网络可靠支持高采样率（88.2 kHz+）时启用。",
     showArtistImages: '显示艺术家图片',
     showArtistImagesDesc: '在艺术家概览中加载并显示艺术家图片。默认关闭以减少大型音乐库的服务器磁盘I/O和网络负载。',
     showTrayIcon: '显示托盘图标',