fix(ui): share retail tab state binding

Replace the character window's synthesized tab sprites, labels, colors, and hit panels with the same DAT-authored Open/Closed state path used by Spellbook/Components. Preserve controller-owned page selection while letting UIElement state propagation own tab chrome and typography.

Co-authored-by: OpenAI Codex <codex@openai.com>

src/AcDream.App/UI/Layout/RetailTabBinding.cs

@@ -0,0 +1,39 @@
+using System;
+
+namespace AcDream.App.UI.Layout;
+
+/// <summary>
+/// Shared controller seam for retail DAT-authored tabs. The LayoutDesc owns the
+/// tab's font, colors, and child chrome; controllers only bind activation and
+/// select the retail <c>Open</c>/<c>Closed</c> state.
+/// </summary>
+internal static class RetailTabBinding
+{
+    public static void SetClick(UiElement? element, Action? action)
+    {
+        if (element is null) return;
+
+        element.ClickThrough = action is null;
+        switch (element)
+        {
+            case UiButton button: button.OnClick = action; break;
+            case UiText text: text.OnClick = action; break;
+            case UiDatElement dat: dat.OnClick = action; break;
+        }
+    }
+
+    public static bool SetOpen(UiElement? element, bool open)
+    {
+        if (element is IUiDatStateful stateful
+            && stateful.TrySetRetailState(open ? RetailUiStateIds.Open : RetailUiStateIds.Closed))
+            return true;
+
+        if (element is UiButton button)
+        {
+            button.Selected = open;
+            return true;
+        }
+
+        return false;
+    }
+}