fix(queue): restore drag-and-drop reordering on macOS (#453)

c1c151ee added `-webkit-user-select: none` to <body>; on macOS WKWebView this
also blocks dragstart on the draggable .queue-track rows (WebKit couples
selectability with draggability), so queue reordering and its blue insertion
line silently broke. Marking the rows as `-webkit-user-drag: element` restores
drag initiation. WebKitGTK (Linux) is unaffected. Needs confirmation on a Mac.

cc

src/lib/components/QueuePanel.svelte

@@ -878,6 +878,12 @@
     border-radius: 6px;
     cursor: pointer;
     transition: background-color 150ms ease;
+    /* macOS/WKWebView couples draggability with selectability: the inherited
+       `-webkit-user-select: none` on <body> blocks dragstart on these rows, so
+       queue reordering (and its blue insertion line) silently broke on macOS
+       (#453). Marking the row as a drag element restores it. WebKitGTK (Linux)
+       is unaffected. */
+    -webkit-user-drag: element;
   }
 
   .queue-track:hover {