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/nl.ts

@@ -541,6 +541,13 @@ export const nlTranslation = {
     infiniteQueue: 'Oneindige wachtrij',
     infiniteQueueDesc: 'Automatisch willekeurige nummers toevoegen als de wachtrij leeg raakt',
     experimental: 'Experimenteel',
+    seekbarStyle: 'Zoekbalkstijl',
+    seekbarStyleDesc: 'Kies het uiterlijk van de afspeelbalk',
+    seekbarWaveform: 'Golfvorm',
+    seekbarLinedot: 'Lijn & punt',
+    seekbarBar: 'Balk',
+    seekbarThick: 'Dikke balk',
+    seekbarSegmented: 'Gesegmenteerd',
   },
   changelog: {
     modalTitle: 'Wat is nieuw',