fix(ui): retail scrollbar parity — button seating, full-track thumb, hover/pressed states

Owner report (2026-08-24): our scrollbar arrows pointed the wrong way,
the thumb vanished when there was nothing to scroll, and neither the
thumb nor the arrow buttons reacted to hover/press.

All three are one retail mechanism we had not ported:

1. Seating: UIElement_Scrollbar::UpdateScrollingArea @0x00470AA0 moves
   the INCREMENT designee (attribute 0x77) to the top/left corner and
   the DECREMENT designee (0x78) to the bottom/right, ignoring authored
   positions. The vertical base skin (0x10000455 in layout 0x2100003E)
   authors the DOWN-arrow decrement at Y=0 and the UP-arrow increment
   at Y=32 (live-DAT probed; sprite art visually verified from decoded
   PNGs), so our authored-Y ordering drew both arrows upside down.
   DatWidgetFactory now seats by designation; the hand-wired sites
   (CharacterStatController, ExternalContainerController, the
   Config/Vendor menu chrome) share the new RetailScrollbarChrome
   catalog instead of local constants.

2. Full-track thumb: UpdateLayout @0x004710d0 sizes the thumb from
   proportion attribute 0x88, which DEFAULTS to 1.0 — a content-fits
   bar shows a thumb filling the whole track; disabled only removes
   input and the page regions. Our draw skipped the thumb entirely on
   !HasOverflow.

3. States: every arrow button and thumb slice authors Normal (red gem /
   dark navy), Normal_rollover (amber gem / bright blue) and
   Normal_pressed (gold highlight / dark) media. The widget now tracks
   thumb hover and selects rollover media on hover and pressed media
   while dragging; the factory extracts the thumb-state media for both
   the 3-slice and single-sprite thumb shapes.

ScrollbarSkinLiveDatTests pins the designations and state media against
the installed DAT so a revision or importer regression fails loudly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -471,6 +471,108 @@ public class UiScrollbarTests
         Assert.Equal(expectedWidth, width, 3);
     }
 
+    /// <summary>
+    /// 2026-08-24 owner report: retail shows a thumb FILLING the whole
+    /// track when there is nothing to scroll — the proportion attribute
+    /// 0x88 defaults to 1.0 in <c>UIElement_Scrollbar::UpdateLayout
+    /// @0x004710d0</c>, so a content-fits bar sizes the widget to the full
+    /// scrolling area; only input goes away with the disabled state. The
+    /// previous draw skipped the thumb entirely on <c>!HasOverflow</c>.
+    /// </summary>
+    [Fact]
+    public void NoOverflow_DrawsAFullTrackThumb()
+    {
+        var device = new RecordingGpuDevice();
+        var renderer = new TextRenderer(device, new NullGpuFrameSource(), "unused");
+        renderer.Begin(new Vector2(800f, 600f));
+        var ctx = new UiRenderContext(renderer, new Vector2(800f, 600f));
+
+        const uint topTex = 60u, midTex = 63u, botTex = 66u;
+        var model = new UiScrollable { ContentHeight = 150, ViewHeight = 150 };
+        var bar = new UiScrollbar
+        {
+            Width = 16f,
+            Height = 200f,
+            SpriteResolve = id => id is topTex or midTex or botTex ? (id, 16, 3) : (0u, 0, 0),
+            ThumbTopSprite = topTex,
+            ThumbSprite = midTex,
+            ThumbBotSprite = botTex,
+            Model = model,
+        };
+        Assert.True(bar.IsModelDisabled);
+
+        bar.DrawSelfAndChildren(ctx);
+
+        // Top cap sits at the top of the track (below the 16px up button)…
+        var top = Assert.Single(
+            renderer.DebugSpriteSegmentVerts, s => s.Texture == topTex);
+        float topMinY = Enumerable.Range(0, top.Verts.Count / 8)
+            .Min(i => top.Verts[i * 8 + 1]);
+        Assert.Equal(16f, topMinY, 1);
+        // …and the bottom cap ends at the bottom of the track (above the
+        // 16px down button) — a full-track thumb.
+        var bot = Assert.Single(
+            renderer.DebugSpriteSegmentVerts, s => s.Texture == botTex);
+        float botMaxY = Enumerable.Range(0, bot.Verts.Count / 8)
+            .Max(i => bot.Verts[i * 8 + 1]);
+        Assert.Equal(184f, botMaxY, 1);
+    }
+
+    /// <summary>
+    /// 2026-08-24 owner report: hovering the thumb highlights it
+    /// (Normal_rollover media — bright blue on the base skin) and holding a
+    /// drag shows the pressed media (authored to look like the resting
+    /// color). Mirrors retail's authored three-state thumb slices.
+    /// </summary>
+    [Fact]
+    public void ThumbHoverAndDrag_SelectRolloverAndPressedMedia()
+    {
+        var model = new UiScrollable { ContentHeight = 200, ViewHeight = 150, LineHeight = 10 };
+        var bar = new UiScrollbar
+        {
+            Width = 16f,
+            Height = 200f,
+            Model = model,
+            ThumbSprite = 1u,
+            ThumbRolloverSprite = 2u,
+            ThumbPressedSprite = 3u,
+            ThumbTopSprite = 10u,
+            ThumbTopRolloverSprite = 20u,
+            ThumbTopPressedSprite = 30u,
+            ThumbBotSprite = 100u,
+            ThumbBotRolloverSprite = 200u,
+            ThumbBotPressedSprite = 300u,
+        };
+        // Track 16..184 (168px), ratio 0.75 → thumb 16..142 at position 0.
+        Assert.Equal(1u, bar.ActiveThumbSpriteForTest);
+
+        // Hover over the thumb → rollover on every slice.
+        bar.OnEvent(new UiEvent(0u, bar, UiEventType.HoverEnter, Data1: 8, Data2: 50));
+        Assert.Equal(2u, bar.ActiveThumbSpriteForTest);
+        Assert.Equal(20u, bar.ActiveThumbTopSpriteForTest);
+        Assert.Equal(200u, bar.ActiveThumbBotSpriteForTest);
+
+        // Press and hold (drag) → pressed media.
+        bar.OnEvent(new UiEvent(0u, bar, UiEventType.MouseDown, Data1: 8, Data2: 50));
+        Assert.True(bar.IsDragging);
+        Assert.Equal(3u, bar.ActiveThumbSpriteForTest);
+        Assert.Equal(30u, bar.ActiveThumbTopSpriteForTest);
+        Assert.Equal(300u, bar.ActiveThumbBotSpriteForTest);
+
+        // Release while still over the thumb → back to the hover highlight.
+        bar.OnEvent(new UiEvent(0u, bar, UiEventType.MouseUp, Data1: 8, Data2: 50));
+        Assert.Equal(2u, bar.ActiveThumbSpriteForTest);
+
+        // Move to the track BELOW the thumb → back to normal.
+        bar.OnEvent(new UiEvent(0u, bar, UiEventType.MouseMove, Data1: 8, Data2: 170));
+        Assert.Equal(1u, bar.ActiveThumbSpriteForTest);
+
+        // Leave the bar entirely → normal.
+        bar.OnEvent(new UiEvent(0u, bar, UiEventType.HoverEnter, Data1: 8, Data2: 50));
+        bar.OnEvent(new UiEvent(0u, bar, UiEventType.HoverLeave));
+        Assert.Equal(1u, bar.ActiveThumbSpriteForTest);
+    }
+
     private sealed class NullGpuFrameSource : ICurrentGpuFrameSource
     {
         public IGpuFrame? CurrentFrame => null;