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>

tests/AcDream.App.Tests/UI/UiScrollbarTests.cs

@@ -157,6 +157,47 @@ public class UiScrollbarTests
         Assert.Equal(64, model.ScrollY);
     }
 
+    [Fact]
+    public void HorizontalModel_UsesIndependentRolloverAndPressedArrowMedia()
+    {
+        var root = new UiRoot { Width = 300f, Height = 100f };
+        var model = new UiScrollable
+        {
+            ContentHeight = 640,
+            ViewHeight = 320,
+            LineHeight = 32,
+        };
+        var bar = new UiScrollbar
+        {
+            Width = 160f,
+            Height = 36f,
+            Horizontal = true,
+            Model = model,
+            UpSprite = 1u,
+            UpRolloverSprite = 2u,
+            UpPressedSprite = 3u,
+            DownSprite = 4u,
+            DownRolloverSprite = 5u,
+            DownPressedSprite = 6u,
+        };
+        root.AddChild(bar);
+
+        root.OnMouseMove(5, 10);
+        Assert.Equal(2u, bar.ActiveStartSpriteForTest);
+        Assert.Equal(4u, bar.ActiveEndSpriteForTest);
+
+        // Moving between two regions of the same procedural scrollbar must
+        // refresh its sub-control hover, not wait for a whole-widget leave.
+        root.OnMouseMove(155, 10);
+        Assert.Equal(1u, bar.ActiveStartSpriteForTest);
+        Assert.Equal(5u, bar.ActiveEndSpriteForTest);
+
+        root.OnMouseDown(UiMouseButton.Left, 155, 10);
+        Assert.Equal(6u, bar.ActiveEndSpriteForTest);
+        root.OnMouseUp(UiMouseButton.Left, 155, 10);
+        Assert.Equal(5u, bar.ActiveEndSpriteForTest);
+    }
+
     [Fact]
     public void ModelWithoutOverflow_IsDisabledAndHideDisabledSuppressesPresentation()
     {