fix(studio): Character window — selected-row highlight uses retail bar sprite

Replaces the translucent-gold BackgroundColor tint with sprite 0x06001397
(Button state 6 — the retail dark horizontal bars) for the selected-row
background. When spriteResolve is provided to Bind(), clicking a row now
applies BackgroundSprite=0x06001397 + SpriteResolve on that row and clears
it on all others. Falls back to HighlightBg tint when no resolver is passed
(tests, or contexts without GL).

UiPanel.BackgroundSprite / SpriteResolve added so any panel can host a
sprite background in place of the solid BackgroundColor rect. HandleRowClick
updated to accept spriteResolve and apply the sprite or tint branch
depending on availability. Two new tests verify the sprite / deselect paths.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/AcDream.App.Tests/UI/Layout/CharacterStatControllerTests.cs

@@ -433,6 +433,45 @@ public class CharacterStatControllerTests
         Assert.Equal(0f, rows[2].BackgroundColor.W);
     }
 
+    [Fact]
+    public void RowClick_WithSpriteResolve_SelectedRowHasHighlightSprite()
+    {
+        // When spriteResolve is provided, the selected row must use sprite 0x06001397
+        // (retail Button-state-6 dark bar) instead of the translucent gold BackgroundColor.
+        var list   = new UiPanel();
+        var layout = Fake((CharacterStatController.ListBoxId, list));
+
+        // Minimal sprite resolver — returns a fake non-zero handle so UiPanel draws it.
+        static (uint, int, int) FakeResolve(uint id) => (1u, 32, 8);
+
+        CharacterStatController.Bind(layout, SampleData.SampleCharacter,
+            spriteResolve: FakeResolve);
+
+        var rows = list.Children.OfType<UiClickablePanel>().ToList();
+        rows[2].OnClick!();
+
+        Assert.Equal(0x06001397u, rows[2].BackgroundSprite);    // selected → sprite
+        Assert.Equal(0f,          rows[2].BackgroundColor.W);   // no tint
+        Assert.Equal(0u,          rows[0].BackgroundSprite);    // others cleared
+        Assert.Equal(0u,          rows[1].BackgroundSprite);
+    }
+
+    [Fact]
+    public void RowClick_WithSpriteResolve_Deselect_ClearsSprite()
+    {
+        var list   = new UiPanel();
+        var layout = Fake((CharacterStatController.ListBoxId, list));
+        static (uint, int, int) FakeResolve(uint id) => (1u, 32, 8);
+        CharacterStatController.Bind(layout, SampleData.SampleCharacter,
+            spriteResolve: FakeResolve);
+
+        var rows = list.Children.OfType<UiClickablePanel>().ToList();
+        rows[2].OnClick!();   // select
+        rows[2].OnClick!();   // deselect
+
+        Assert.Equal(0u, rows[2].BackgroundSprite);
+    }
+
     // ── Pass 2: Raise button affordability ───────────────────────────────────
 
     [Fact]