feat(ui): D.2b-B — UiMeter vertical fill (burden bar, retail m_eDirection 2/4)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,35 @@
+using AcDream.App.UI;
+using Xunit;
+
+namespace AcDream.App.Tests.UI;
+
+public class UiMeterVerticalTests
+{
+    [Fact]
+    public void Vertical_fill_from_bottom_occupies_lower_fraction()
+    {
+        // 11x58 bar, 50% → fill rect is the bottom 29px.
+        var (x, y, w, h) = UiMeter.ComputeVFillRect(0.5f, 11f, 58f, fromBottom: true);
+        Assert.Equal(0f, x);
+        Assert.Equal(29f, y, 3);    // h - h*p = 58 - 29
+        Assert.Equal(11f, w);
+        Assert.Equal(29f, h, 3);
+    }
+
+    [Fact]
+    public void Vertical_fill_from_top_starts_at_zero()
+    {
+        var (_, y, _, h) = UiMeter.ComputeVFillRect(0.25f, 11f, 58f, fromBottom: false);
+        Assert.Equal(0f, y);
+        Assert.Equal(14.5f, h, 3);
+    }
+
+    [Theory]
+    [InlineData(-1f, 0f)]
+    [InlineData(2f, 58f)]
+    public void Vertical_fill_clamps_fraction(float pct, float expectedH)
+    {
+        var (_, _, _, h) = UiMeter.ComputeVFillRect(pct, 11f, 58f, fromBottom: true);
+        Assert.Equal(expectedH, h, 3);
+    }
+}