fix(app): slice 7 fix round B item 10 — no row-selection band on column grids

VVS's own HudList grids (Monsters/Meta/Route/Items and every other
<list><column> grid this codebase has, present and future) have no
row-selection highlight at all — only the per-cell click callbacks are a
real VTank concept. UiMarkupList.DrawColumns painted a SelectedColor band
under the selected row anyway (a holdover from the legacy single-column
list path, which keeps its own band unchanged — that's a plain list, not a
VVS grid). Removed the band draw from DrawColumns only; SelectedIndexSource
still drives scroll-into-view, and every onclick/onchange callback is
untouched.

New test: ColumnGrids_NeverDrawARowSelectionBand (a column list with a
real in-range selected index must never paint SelectedColor). Mutation
check: before the fix this test was RED against the real code
("expected no SelectedColor fill in a column-based grid"); after removing
the band draw it's green.

tests/AcDream.Plugins.MossTank.Tests: 671/671 (unchanged — this is an
App-layer fix, MossTank markup only consumes the existing <column>
grammar).
tests/AcDream.App.Tests --filter Markup|Plugin|UiMenu|Slider: 277/3 skipped/280 (was 276/3/279, +1 new test).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/AcDream.App/UI/UiMarkupList.cs

@@ -320,12 +320,17 @@ public sealed class UiMarkupList : UiElement
         context.DrawFill(0f, 0f, Width, Height, BackgroundColor);
         context.DrawRectOutline(0f, 0f, Width, Height, BorderColor, 1f);
 
+        // Fix round B item 10 (owner/oracle: VVS's own HudList grids have NO
+        // row-selection highlight at all — Monsters/Meta/Route/Items and
+        // every other <list><column> grid). SelectedIndexSource above still
+        // drives scroll-into-view; the SelectedColor band draw the legacy
+        // single-column path (below, unaffected) uses is deliberately
+        // skipped here. Every per-cell onclick/onchange callback is
+        // unchanged — only the visual band is gone.
         int end = Math.Min(rowCount, _topRow + visibleRows);
         for (int index = _topRow; index < end; index++)
         {
             float y = (index - _topRow) * RowHeight;
-            if (index == selected)
-                context.DrawFill(1f, y + 1f, Width - 2f, RowHeight - 1f, SelectedColor);
 
             for (int c = 0; c < columns.Count; c++)
             {

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

@@ -551,6 +551,50 @@ public sealed class MarkupListColumnsTests
             "expected col0's icon clamped inside the 50px list width");
     }
 
+    [Fact]
+    public void ColumnGrids_NeverDrawARowSelectionBand()
+    {
+        // Fix round B item 10 (owner/oracle: VVS's own HudList grids —
+        // Monsters/Meta/Route/Items and every other <list><column> grid —
+        // have no row-selection highlight at all; only the per-cell click
+        // callbacks survive). DrawColumns must never paint SelectedColor,
+        // even when SelectedIndexSource reports a real in-range row.
+        var list = new UiMarkupList
+        {
+            Width = 100f, Height = 60f, RowHeight = 18f,
+            SelectedIndexSource = () => 1,
+            BackgroundColor = new Vector4(0f, 0f, 0f, 1f),
+            BorderColor = default,
+            SelectedColor = new Vector4(1f, 0f, 0f, 1f), // distinct, unmistakable
+            Columns = new[]
+            {
+                UiMarkupListColumn.Text(100f, () => new[] { "Row0", "Row1", "Row2" }, null),
+            },
+        };
+        var (renderer, ctx) = MakeContext(200f, 200f);
+
+        list.DrawSelfAndChildren(ctx);
+
+        bool anySelectedFill = renderer.DebugSpriteSegmentVerts.Any(s =>
+        {
+            if (s.Texture != 0u)
+                return false;
+            for (int q = 0; q + 48 <= s.Verts.Count; q += 48)
+            {
+                float r = s.Verts[q + 4], g = s.Verts[q + 5], b = s.Verts[q + 6], a = s.Verts[q + 7];
+                if (MathF.Abs(r - list.SelectedColor.X) < 0.01f
+                    && MathF.Abs(g - list.SelectedColor.Y) < 0.01f
+                    && MathF.Abs(b - list.SelectedColor.Z) < 0.01f
+                    && MathF.Abs(a - list.SelectedColor.W) < 0.01f)
+                {
+                    return true;
+                }
+            }
+            return false;
+        });
+        Assert.False(anySelectedFill, "expected no SelectedColor fill in a column-based grid");
+    }
+
     // ── Draw-level: column x-offsets, check glyph, icon, clipping ────────────
 
     private static (TextRenderer renderer, UiRenderContext ctx) MakeContext(float w, float h)