Persist vinyl rotation angle across page reloads

- Save current rotation angle to localStorage every 2s and on page unload
- Restore angle on page load via CSS custom property --vinyl-offset
- Extract angle from computed transform matrix

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

media_server/static/css/styles.css

@@ -628,8 +628,8 @@ h1 {
 }
 
 @keyframes vinylSpin {
-    from { transform: rotate(0deg); }
-    to { transform: rotate(360deg); }
+    from { transform: rotate(var(--vinyl-offset, 0deg)); }
+    to { transform: rotate(calc(var(--vinyl-offset, 0deg) + 360deg)); }
 }
 
 .track-info {