feat(ui): D.5.3/B.2 — spine: drag-lift hook + ghost snapshot (full opacity) + drop-on-hit-only

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/UI/IItemListDragHandler.cs

@@ -11,6 +11,12 @@ namespace AcDream.App.UI;
 /// </summary>
 public interface IItemListDragHandler
 {
+    /// <summary>The drag STARTED from a cell in this list — retail's RecvNotice_ItemListBeginDrag
+    /// → RemoveShortcut (decomp 0x004bd930/0x004bd450): the handler removes the lifted item from its
+    /// model + wire so the source slot empties immediately. The item is "in hand" until
+    /// HandleDropRelease (place) or the drag ends off-target (stays removed). No restore on cancel.</summary>
+    void OnDragLift(UiItemList sourceList, UiItemSlot sourceCell, ItemDragPayload payload);
+
     /// <summary>True ⇒ the target cell shows the accept (green) frame; false ⇒ reject (red).</summary>
     bool OnDragOver(UiItemList targetList, UiItemSlot targetCell, ItemDragPayload payload);