fix(ui): complete retail inventory scroll polish

Preserve pixel scroll offsets across inventory rebuilds, crop partially visible rows with nested geometry/UV clips, and replace the obsolete 560px resize ceiling with available screen height. Keep retail's row-sized wheel step while allowing continuous scrollbar thumb positions.

Co-Authored-By: Codex <codex@openai.com>

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

@@ -0,0 +1,36 @@
+using AcDream.App.UI;
+using Xunit;
+
+namespace AcDream.App.Tests.UI;
+
+public sealed class UiClipRectTests
+{
+    [Fact]
+    public void TryClipSprite_cropsGeometryAndMatchingUvs()
+    {
+        var clip = new UiClipRect(0f, 0f, 100f, 100f);
+        float x = -8f, y = 88f, w = 32f, h = 32f;
+        float u0 = 0f, v0 = 0f, u1 = 1f, v1 = 1f;
+
+        bool visible = UiClipRect.TryClipSprite(
+            clip, ref x, ref y, ref w, ref h, ref u0, ref v0, ref u1, ref v1);
+
+        Assert.True(visible);
+        Assert.Equal((0f, 88f, 24f, 12f), (x, y, w, h));
+        Assert.Equal((0.25f, 0f, 1f, 0.375f), (u0, v0, u1, v1));
+    }
+
+    [Fact]
+    public void Intersection_andFullyOutsideSprite_areEmpty()
+    {
+        UiClipRect intersection = UiClipRect.Intersect(
+            new UiClipRect(0f, 0f, 20f, 20f),
+            new UiClipRect(30f, 30f, 40f, 40f));
+        float x = 0f, y = 0f, w = 10f, h = 10f;
+        float u0 = 0f, v0 = 0f, u1 = 1f, v1 = 1f;
+
+        Assert.True(intersection.IsEmpty);
+        Assert.False(UiClipRect.TryClipSprite(
+            intersection, ref x, ref y, ref w, ref h, ref u0, ref v0, ref u1, ref v1));
+    }
+}