playlists(#37): drag-and-drop reorder in the Playlists management tab

Videos within a playlist can now be dragged to reorder (desktop), on top of the
↑/↓ buttons kept for touch/accessibility. HTML5 DnD delegated on the list:
dragstart records the row's playlist + index, dragover highlights the drop
target (accent inset bar) and allows the drop, drop reorders via
reorderPlaylistItems and publishes optimistically. Drag is scoped to a single
playlist (can't cross playlists); dragging row dims to 0.5; grab/grabbing cursor.

Lint + build clean; profile-modal-controller tests 26/26.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

css/tailwind.source.css

@@ -3137,6 +3137,19 @@
     display: flex;
     align-items: center;
     gap: var(--space-sm);
+    cursor: grab;
+  }
+
+  .playlist-video:active {
+    cursor: grabbing;
+  }
+
+  .playlist-video--dragging {
+    opacity: 0.5;
+  }
+
+  .playlist-video--drop-target {
+    box-shadow: inset 0 var(--size-2px) 0 0 var(--color-accent);
   }
 
   .playlist-video__title {