perf: reduce CPU usage and unify next-track buffering settings

- Throttle audio:progress from 100ms to 500ms; WaveformSeek and
  FsSeekbar use imperative DOM updates instead of React re-renders
- Fix all usePlayerStore() calls without selectors across pages and
  components (useShallow / individual selectors throughout)
- Remove filter:blur and transform:scale from Hero, AlbumDetail and
  FullscreenPlayer backgrounds — eliminated expensive software
  compositing layers on WebKitGTK
- Replace translate3d with 2D translate in FS mesh and portrait
  animations; remove will-change:transform from mesh blobs
- Move Hot Cache section from Storage tab to Audio tab; group Preload
  and Hot Cache under a shared 'Next Track Buffering' section with a
  mutual-exclusivity note and auto-disable logic
- Add 'off' toggle to Preload (replaces Off button with toggle switch);
  enabling either method now automatically disables the other

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

src/locales/de.ts

@@ -571,6 +571,9 @@ export const deTranslation = {
     gaplessDesc: 'Nächsten Track vorpuffern um Lücken zwischen Songs zu vermeiden',
     preloadMode: 'Nächsten Track vorpuffern',
     preloadModeDesc: 'Wann mit dem Puffern des nächsten Tracks begonnen werden soll',
+    nextTrackBufferingTitle: 'Nächster Track – Pufferung',
+    preloadHotCacheMutualExclusive: 'Preload und Hot Cache erfüllen denselben Zweck – nur eine Methode kann gleichzeitig aktiv sein. Das Aktivieren einer deaktiviert die andere automatisch.',
+    preloadOff: 'Aus',
     preloadBalanced: 'Ausgewogen (30 s vor Ende)',
     preloadEarly: 'Früh (nach 5 s Wiedergabe)',
     preloadCustom: 'Benutzerdefiniert',