refactor(D.2b): DatWidgetFactory review fixes — single lookup + malformed-meter trace

Fix 1: SliceIds now projects the File id during Select rather than calling
TryGetValue twice (once in Where, once in the local File() helper). Added a
comment noting that OrderBy is stable so X-tie order follows insertion order.

Fix 2: BuildMeter emits a [D.2b] Console.WriteLine when the Type-3 container
count is not exactly 2, surfacing malformed or non-vitals meter elements during
Task 8 conformance testing without disturbing the existing solid-color fallback.

Fix 3: Test 5 adds two explicit NotEqual assertions confirming the
ShowDetail-only overlay sprite (OverlayFile = 0x06007490) did not leak into
FrontRight or FrontTile.

5/5 tests pass, 0 warnings.

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

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

@@ -108,5 +108,8 @@ public class DatWidgetFactoryTests
         Assert.Equal(FrontL, m.FrontLeft);
         Assert.Equal(FrontT, m.FrontTile);
         Assert.Equal(FrontR, m.FrontRight);
+        // Overlay (ShowDetail-only, no DirectState "") must not leak into any slice slot.
+        Assert.NotEqual(OverlayFile, m.FrontRight);
+        Assert.NotEqual(OverlayFile, m.FrontTile);
     }
 }