fix: drag-and-drop — set draggable upfront, add Firefox setData, fix duplicate dragend

draggable=true must be set before any mouse event (not on mousedown).
Firefox requires setData() for drag to work. Removed duplicate dragend
listener that was resetting draggable=false and conflicting with the first.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/views.js

@@ -558,19 +558,23 @@ function _initPlaylistDragDrop(container, songs, pl) {
     handle.innerHTML = '<svg width="10" height="14" viewBox="0 0 10 14" fill="currentColor"><circle cx="3" cy="2" r="1.3"/><circle cx="7" cy="2" r="1.3"/><circle cx="3" cy="7" r="1.3"/><circle cx="7" cy="7" r="1.3"/><circle cx="3" cy="12" r="1.3"/><circle cx="7" cy="12" r="1.3"/></svg>';
     item.insertBefore(handle, item.firstChild);
     item._songRef = songs[i];
+    item.draggable = true; // set upfront so browser registers it before any event
 
     item.addEventListener('dragstart', e => {
       if (!e.target.closest('.pl-drag-handle')) { e.preventDefault(); return; }
       dragSrc = item;
       e.dataTransfer.effectAllowed = 'move';
+      e.dataTransfer.setData('text/plain', ''); // required by Firefox
       setTimeout(() => item.classList.add('dragging'), 0);
     });
     item.addEventListener('dragend', () => {
+      dragSrc = null;
       item.classList.remove('dragging');
       container.querySelectorAll('.drag-over').forEach(el => el.classList.remove('drag-over'));
     });
     item.addEventListener('dragover', e => {
       e.preventDefault();
+      e.dataTransfer.dropEffect = 'move';
       if (item === dragSrc) return;
       container.querySelectorAll('.drag-over').forEach(el => el.classList.remove('drag-over'));
       item.classList.add('drag-over');
@@ -580,6 +584,7 @@ function _initPlaylistDragDrop(container, songs, pl) {
     });
     item.addEventListener('drop', e => {
       e.preventDefault();
+      e.stopPropagation();
       if (!dragSrc || item === dragSrc) return;
       item.classList.remove('drag-over');
       const allItems = Array.from(container.children);
@@ -594,13 +599,10 @@ function _initPlaylistDragDrop(container, songs, pl) {
         const n = el.querySelector('.song-num');
         if (n) n.textContent = idx + 1;
       });
-      // Debounced save
+      // Debounced save to Navidrome
       clearTimeout(saveTimer);
       saveTimer = setTimeout(() => _savePlaylistOrder(pl, songs), 800);
     });
-
-    handle.addEventListener('mousedown', () => { item.draggable = true; });
-    item.addEventListener('dragend', () => { item.draggable = false; });
   });
 }