feat(ui): D.5.3/B.1 — toolbar drag handler stub + spine wiring (TS-33)

Implements Task 4 of the drag-drop spine: ToolbarController now satisfies
IItemListDragHandler. The ctor loop wires RegisterDragHandler(this) on every
slot list and stamps Cell.SlotIndex + Cell.SourceKind=ShortcutBar, matching
retail's gmToolbarUI::PostInit/RegisterItemListDragHandler pattern. OnDragOver
accepts any non-empty payload (TS-33 stub; eligibility gate is Stream B.2).
HandleDropRelease logs and returns (no AddShortcut 0x019C / RemoveShortcut
0x019D wire yet). Three new B.1 xUnit tests cover handler registration, accept,
and inert-stub semantics. All 490 app tests pass.

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

tests/AcDream.App.Tests/UI/Layout/ToolbarControllerTests.cs

@@ -421,4 +421,61 @@ public class ToolbarControllerTests
 
         Assert.Equal(callsAfterBind, iconCallCount); // unchanged
     }
+
+    // ── B.1: drag-drop spine wiring ──────────────────────────────────────────
+
+    /// <summary>Bind registers the controller as each slot list's drag handler and
+    /// stamps every cell's SlotIndex + SourceKind=ShortcutBar.</summary>
+    [Fact]
+    public void Bind_registersDragHandler_andStampsSlots()
+    {
+        var (layout, slots, _) = FakeToolbar();
+        var repo = new ClientObjectTable();
+
+        var ctrl = ToolbarController.Bind(layout, repo,
+            () => Array.Empty<PlayerDescriptionParser.ShortcutEntry>(),
+            iconIds: (_,_,_,_,_) => 0u, useItem: _ => { });
+
+        for (int i = 0; i < Row1.Length; i++)
+        {
+            Assert.Same(ctrl, slots[Row1[i]].DragHandler);
+            Assert.Equal(i, slots[Row1[i]].Cell.SlotIndex);
+            Assert.Equal(ItemDragSource.ShortcutBar, slots[Row1[i]].Cell.SourceKind);
+        }
+        // Bottom row slots are indices 9..17.
+        for (int j = 0; j < Row2.Length; j++)
+            Assert.Equal(9 + j, slots[Row2[j]].Cell.SlotIndex);
+    }
+
+    /// <summary>OnDragOver accepts a real item (ObjId != 0). Eligibility (IsShortcutEligible)
+    /// is Stream B.2; the stub accepts any non-empty payload.</summary>
+    [Fact]
+    public void OnDragOver_acceptsRealItem()
+    {
+        var (layout, slots, _) = FakeToolbar();
+        var ctrl = ToolbarController.Bind(layout, new ClientObjectTable(),
+            () => Array.Empty<PlayerDescriptionParser.ShortcutEntry>(),
+            iconIds: (_,_,_,_,_) => 0u, useItem: _ => { });
+
+        var list = slots[Row1[0]];
+        var payload = new ItemDragPayload(0x5001u, ItemDragSource.Inventory, 0, new UiItemSlot());
+        Assert.True(ctrl.OnDragOver(list, list.Cell, payload));
+    }
+
+    /// <summary>HandleDropRelease is a logging stub (TS-33): it must not throw and must not
+    /// mutate the target slot (no wire / no store yet).</summary>
+    [Fact]
+    public void HandleDropRelease_isInertStub()
+    {
+        var (layout, slots, _) = FakeToolbar();
+        var ctrl = ToolbarController.Bind(layout, new ClientObjectTable(),
+            () => Array.Empty<PlayerDescriptionParser.ShortcutEntry>(),
+            iconIds: (_,_,_,_,_) => 0u, useItem: _ => { });
+
+        var list = slots[Row1[2]];
+        var payload = new ItemDragPayload(0x5001u, ItemDragSource.ShortcutBar, 0, new UiItemSlot());
+        var ex = Record.Exception(() => ctrl.HandleDropRelease(list, list.Cell, payload));
+        Assert.Null(ex);
+        Assert.Equal(0u, list.Cell.ItemId);    // unchanged — inert stub
+    }
 }