fix(ui): port retail item drag visuals

Keep retail's underlay-free m_pDragIcon separate from the full cell icon and reveal the authored ghost mesh on physical source cells for the complete drag lifecycle. This removes the backpack backing from the cursor and retires AP-47.

Co-Authored-By: Codex <codex@openai.com>

tests/AcDream.App.Tests/UI/DragDropSpineTests.cs

@@ -76,6 +76,16 @@ public class DragDropSpineTests
         Assert.Equal(32, g.Value.h);
     }
 
+    [Fact]
+    public void GetDragGhost_prefersDedicatedUnderlayFreeTexture()
+    {
+        var cell = new UiItemSlot { Width = 36, Height = 36 }; // retail bag cell is larger than its icon
+        cell.SetItem(0x5001u, 0x99u, dragIconTexture: 0x77u);
+
+        Assert.Equal((0x77u, 32, 32), cell.GetDragGhost());
+        Assert.Equal(0x99u, cell.IconTexture); // source cell keeps the full m_pIcon
+    }
+
     // ── cell drop-target: DragEnter overlay + DropReleased dispatch ──────────
     private static (UiItemList list, UiItemSlot cell, SpyHandler h) ListWithHandler()
     {
@@ -187,6 +197,32 @@ public class DragDropSpineTests
         Assert.Null(root.DragSource);              // cleaned up
     }
 
+    [Fact]
+    public void InventoryDrag_ghostsSourceUntilRelease()
+    {
+        var (root, _, cell) = RootWithBoundSlot(0x5001u);
+        cell.SourceKind = ItemDragSource.Inventory;
+
+        root.OnMouseDown(UiMouseButton.Left, 10, 10);
+        root.OnMouseMove(20, 10);
+        Assert.True(cell.WaitingVisual);
+
+        root.OnMouseUp(UiMouseButton.Left, 600, 500);
+        Assert.False(cell.WaitingVisual);
+    }
+
+    [Fact]
+    public void ShortcutDrag_doesNotGhostSource()
+    {
+        var (root, _, cell) = RootWithBoundSlot(0x5001u);
+        cell.SourceKind = ItemDragSource.ShortcutBar;
+
+        root.OnMouseDown(UiMouseButton.Left, 10, 10);
+        root.OnMouseMove(20, 10);
+
+        Assert.False(cell.WaitingVisual);
+    }
+
     // ── Full UiRoot chain: arming + use-vs-drag ─────────────────────────────
     // A bound, hit-testable slot inside a list, sized for the hit-test.
     private static (UiRoot root, UiItemList list, UiItemSlot cell) RootWithBoundSlot(uint itemId)

tests/AcDream.App.Tests/UI/UiItemSlotTests.cs

@@ -12,6 +12,10 @@ public class UiItemSlotTests
     public void DefaultEmptySprite_isToolbarBorder()
         => Assert.Equal(0x060074CFu, new UiItemSlot().EmptySprite);
 
+    [Fact]
+    public void DefaultWaitingSprite_isRetailGhostMesh()
+        => Assert.Equal(0x0600109Au, new UiItemSlot().WaitingSprite);
+
     [Fact]
     public void Empty_whenNoItem()
     {