fix(ui): resolve retail spell slot background

Keep shared shortcut digit overlays separate from the per-ItemList background. Resolve the magic favorite list through its cross-layout inherited cell prototype and use the pinned brown/gold ItemSlot_Empty surface instead of the blue toolbar slot.

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

src/AcDream.App/UI/UiShortcutDigitGraphics.cs

@@ -0,0 +1,12 @@
+namespace AcDream.App.UI;
+
+/// <summary>
+/// Shared DAT digit overlays used by UIItem shortcut cells. Both gmToolbarUI and
+/// gmSpellcastingUI call UIElement_UIItem::SetShortcutNum @ 0x004E1590, so they
+/// share these number arrays. The underlying ItemSlot_Empty surface remains a
+/// per-ItemList asset selected by that list's cell prototype.
+/// </summary>
+public sealed record UiShortcutDigitGraphics(
+    uint[]? RegularDigits,
+    uint[]? GhostedDigits,
+    uint[]? EmptyDigits);