feat(D.5.1): ToolbarController — bind 18 slots, populate, deferred rebind, click-to-use

Port of gmToolbarUI::PostInit (slot wiring) + UpdateFromPlayerDesc (flush-and-bind
shortcuts from PlayerDescription) + SetDelayedShortcutNum (deferred ItemAdded rebind)
+ UseShortcut (click → useItem callback).

UiItemSlot gains Clicked (Action?) + OnEvent override (MouseDown → Clicked?.Invoke())
matching the retail UIElement_UIItem click dispatch pattern. UiEvent is a positional
record struct so the OnEvent override reads e.Type (int) against UiEventType.MouseDown
(const int 0x201) — confirmed from UiEvent.cs + UiText.cs before writing.

Three tests green (populate bound slot, deferred rebind on ItemAdded, click fires useItem).
Full suite: 0 failures.

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

src/AcDream.App/UI/UiItemSlot.cs

@@ -37,6 +37,17 @@ public sealed class UiItemSlot : UiElement
 
     public void Clear() { ItemId = 0; IconTexture = 0; }
 
+    /// <summary>Invoked by <see cref="OnEvent"/> when a left-button-down lands on
+    /// a bound slot. Wired by <c>ToolbarController</c> to the use-item callback.</summary>
+    public Action? Clicked { get; set; }
+
+    /// <inheritdoc/>
+    public override bool OnEvent(in UiEvent e)
+    {
+        if (e.Type == UiEventType.MouseDown) { Clicked?.Invoke(); return true; }
+        return false;
+    }
+
     protected override void OnDraw(UiRenderContext ctx)
     {
         if (ItemId != 0 && IconTexture != 0)