feat(seekbar): configurable seekbar styles with animated preview

Add five seekbar styles selectable in Settings → Appearance:
Waveform, Line & Dot, Bar, Thick Bar, and Segmented. Each option
shows an animated canvas preview using requestAnimationFrame.

Style is persisted in authStore (seekbarStyle, default: waveform).
Translations added for all 7 languages.

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

src/locales/en.ts

@@ -544,6 +544,13 @@ export const enTranslation = {
     infiniteQueue: 'Infinite Queue',
     infiniteQueueDesc: 'Automatically append random tracks when the queue runs out',
     experimental: 'Experimental',
+    seekbarStyle: 'Seekbar Style',
+    seekbarStyleDesc: 'Choose the look of the player seek bar',
+    seekbarWaveform: 'Waveform',
+    seekbarLinedot: 'Line & Dot',
+    seekbarBar: 'Bar',
+    seekbarThick: 'Thick Bar',
+    seekbarSegmented: 'Segmented',
   },
   changelog: {
     modalTitle: "What's New",