fix(ui): match retail spell bar controls

Place favorite-bar arrows by their authored sides, import rollover and pressed media through the shared scrollbar, and preserve manual offsets across passive refreshes. Carry the mixed-parent DAT anchor chain to a fixed 18-cell favorite viewport so overflow controls and the Cast button remain inside the retail-sized combat frame.

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

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

@@ -0,0 +1,49 @@
+namespace AcDream.App.UI.Layout;
+
+/// <summary>Retail geometry policy for the shared melee/missile/magic combat root.</summary>
+internal static class RetailCombatLayout
+{
+    internal const int VisibleFavoriteSlots = 18;
+    internal const float FavoriteCellWidth = 32f;
+
+    /// <summary>
+    /// Resize the imported combat tree so its favorite list exposes exactly the
+    /// requested number of cells. The DAT deliberately authors the outer combat
+    /// root at 610 pixels while the magic page's descendants use an 800-pixel
+    /// design parent. Retail <c>UIElement::UpdateForParentSizeChange @
+    /// 0x00462640</c> carries that width delta through every raw-edge policy.
+    /// Applying the same chain and solving for the list viewport keeps the
+    /// endowment, arrows, list, Cast button, and outer frame in one coherent
+    /// retained layout instead of resizing individual controls ad hoc.
+    /// </summary>
+    internal static float FitFavoriteSlots(
+        ImportedLayout layout,
+        int visibleSlots = VisibleFavoriteSlots,
+        float cellWidth = FavoriteCellWidth)
+    {
+        ArgumentNullException.ThrowIfNull(layout);
+        if (visibleSlots < 1)
+            throw new ArgumentOutOfRangeException(nameof(visibleSlots));
+        if (!(cellWidth > 0f) || !float.IsFinite(cellWidth))
+            throw new ArgumentOutOfRangeException(nameof(cellWidth));
+
+        UiElement root = layout.Root;
+        ApplyDescendantLayout(root);
+        if (layout.FindElement(SpellcastingUiController.FavoriteListId) is not UiItemList list)
+            throw new InvalidOperationException("Retail combat layout has no favorite spell list.");
+
+        float targetViewport = visibleSlots * cellWidth;
+        root.Width = MathF.Max(0f, root.Width + targetViewport - list.Width);
+        ApplyDescendantLayout(root);
+        return root.Width;
+    }
+
+    private static void ApplyDescendantLayout(UiElement parent)
+    {
+        foreach (UiElement child in parent.Children)
+        {
+            child.ApplyAnchor(parent.Width, parent.Height);
+            ApplyDescendantLayout(child);
+        }
+    }
+}