fix(quick-9): set fixed height on queue track items for stable virtualizer scroll

- Add height: 49px and overflow: hidden to .track-item CSS
- Add overflow: hidden to .track-details CSS
- Fixed height ensures lit-virtualizer _scrollSize is stable from first render
- Prevents scrollbar lag on large queues (20k+ tracks) caused by dynamic item size averaging

frontend/src/components/queue-panel/queue-panel.ts

@@ -282,6 +282,8 @@ export class QueuePanel
             user-select: none;
             width: 100%;
             box-sizing: border-box;
+            height: 49px;
+            overflow: hidden;
         }
 
         .track-item:hover {
@@ -317,6 +319,7 @@ export class QueuePanel
             display: flex;
             flex-direction: column;
             gap: 2px;
+            overflow: hidden;
         }
 
         .track-title {