Add Vinyl panel to Focus mode and fix MPRIS volume feedback loop

- Add VinylPanel.svelte with spinning vinyl disc animation
- Album cover slides left when playing to reveal disc
- CSS-based grooves (40 rings) and amber center label
- Vintage typography with "33 1/3 RPM" badge
- Add 'vinyl' as new Focus tab option in ImmersiveHeader
- Fix MPRIS/PipeWire volume feedback loop by checking if volume
  actually changed before calling setVolume

src/routes/+page.svelte

@@ -2528,7 +2528,11 @@
           case 'set_volume': {
             if (typeof payload.volume === 'number') {
               const normalized = Math.max(0, Math.min(1, payload.volume));
-              await playerSetVolume(Math.round(normalized * 100));
+              const newVolume = Math.round(normalized * 100);
+              // Only update if volume actually changed (prevents MPRIS feedback loop)
+              if (newVolume !== volume) {
+                await playerSetVolume(newVolume);
+              }
             }
             break;
           }