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/Layout/DatWidgetFactoryTests.cs

@@ -786,6 +786,61 @@ public class DatWidgetFactoryTests
         Assert.Equal(Thumb, bar.ThumbSprite);
         Assert.Equal(0u, bar.ThumbTopSprite);
         Assert.Equal(0u, bar.ThumbBotSprite);
+        // 2026-08-24: the thumb's own rollover/pressed media survive onto
+        // the widget (hover highlight / held-drag art).
+        Assert.Equal(0x06005A12u, bar.ThumbRolloverSprite);
+        Assert.Equal(0x06005A13u, bar.ThumbPressedSprite);
+    }
+
+    /// <summary>
+    /// 2026-08-24 owner report ("the arrows point in the wrong direction"):
+    /// retail seats scrollbar buttons by DESIGNATION —
+    /// <c>UIElement_Scrollbar::UpdateScrollingArea @0x00470AA0</c> moves the
+    /// INCREMENT designee (attribute 0x77) to the top corner and the
+    /// DECREMENT designee (0x78) to the bottom corner regardless of authored
+    /// position. The real vertical base skin (0x10000455 in layout
+    /// 0x2100003E) authors the DOWN-arrow decrement at Y=0 and the UP-arrow
+    /// increment at Y=32, so the previous authored-Y ordering put the
+    /// down-arrow art on the TOP button.
+    /// </summary>
+    [Fact]
+    public void Type11_VerticalScrollbar_SeatsButtonsByDesignation_NotAuthoredPosition()
+    {
+        const uint DecrementId = 0x10000071u; // DOWN arrow, authored at Y=0
+        const uint IncrementId = 0x10000072u; // UP arrow, authored at Y=32
+        var decrement = new ElementInfo { Id = DecrementId, Type = 1u, Y = 0f, Width = 16f, Height = 16f };
+        decrement.StateMedia["Normal"] = (0x06004C69u, 1);
+        decrement.StateMedia["Normal_rollover"] = (0x06004C6Au, 1);
+        decrement.StateMedia["Normal_pressed"] = (0x06004C6Bu, 1);
+        var increment = new ElementInfo { Id = IncrementId, Type = 1u, Y = 32f, Width = 16f, Height = 16f };
+        increment.StateMedia["Normal"] = (0x06004C6Cu, 1);
+        increment.StateMedia["Normal_rollover"] = (0x06004C6Du, 1);
+        increment.StateMedia["Normal_pressed"] = (0x06004C6Eu, 1);
+
+        var info = new ElementInfo
+        {
+            Type = 11u,
+            Width = 16f,
+            Height = 48f,
+            Children = [decrement, increment],
+        };
+        var state = new UiStateInfo { Id = UiStateInfo.DirectStateId };
+        state.Properties.Values[0x77u] = new UiPropertyValue
+            { Kind = UiPropertyKind.Enum, UnsignedValue = IncrementId };
+        state.Properties.Values[0x78u] = new UiPropertyValue
+            { Kind = UiPropertyKind.Enum, UnsignedValue = DecrementId };
+        info.States[UiStateInfo.DirectStateId] = state;
+
+        var bar = Assert.IsType<UiScrollbar>(DatWidgetFactory.Create(info, NoTex, null));
+
+        // Top slot = the increment designee's UP-arrow media.
+        Assert.Equal(0x06004C6Cu, bar.UpSprite);
+        Assert.Equal(0x06004C6Du, bar.UpRolloverSprite);
+        Assert.Equal(0x06004C6Eu, bar.UpPressedSprite);
+        // Bottom slot = the decrement designee's DOWN-arrow media.
+        Assert.Equal(0x06004C69u, bar.DownSprite);
+        Assert.Equal(0x06004C6Au, bar.DownRolloverSprite);
+        Assert.Equal(0x06004C6Bu, bar.DownPressedSprite);
     }
 
     /// <summary>
@@ -810,6 +865,8 @@ public class DatWidgetFactoryTests
         topCap.States[1u] = new UiStateInfo { Id = 1u, Name = "Normal", Image = new UiImageMedia(Top, 1) };
         var mid = new ElementInfo { Id = 0x10000365u, Type = 3u, Y = 3f, Width = 16f, Height = 10f };
         mid.StateMedia["Normal"] = (Mid, 1);
+        mid.StateMedia["Normal_rollover"] = (0x06004C64u, 1);
+        mid.StateMedia["Normal_pressed"] = (0x06004C65u, 1);
         mid.States[1u] = new UiStateInfo { Id = 1u, Name = "Normal", Image = new UiImageMedia(Mid, 1) };
         var botCap = new ElementInfo { Id = 0x10000366u, Type = 3u, Y = 13f, Width = 16f, Height = 3f };
         botCap.StateMedia["Normal"] = (Bot, 1);
@@ -838,6 +895,9 @@ public class DatWidgetFactoryTests
         Assert.Equal(Top, bar.ThumbTopSprite);
         Assert.Equal(Mid, bar.ThumbSprite);
         Assert.Equal(Bot, bar.ThumbBotSprite);
+        // 2026-08-24: slice rollover/pressed media survive onto the widget.
+        Assert.Equal(0x06004C64u, bar.ThumbRolloverSprite);
+        Assert.Equal(0x06004C65u, bar.ThumbPressedSprite);
     }
 
     [Fact]