fix(windows): cap bar-chart bar width so sparse data doesn't render as a full-plot block

On pages with few data points (e.g. Drive History 'Drives over time' with a single drive), BarRects computed slotWidth = full plot width, making the lone bar ~70% of the plot — a giant solid rectangle. Caps per-bar width at 64px (recharts maxBarSize parity) and recomputes the band so grouped series stay centred. Verified via screenshot. Adds a regression test.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Copilot

apps/windows/TeslaSync.App.Core/Charts/ChartGeometry.cs

@@ -169,6 +169,17 @@ public static IReadOnlyList<RectD> BarRects(
             : Math.Abs(x.RangeEnd - x.RangeStart);
         var bandWidth = Math.Max(1, slotWidth * slotRatio);
         var barWidth = bandWidth / groups;
+
+        // Cap the per-bar width so a single or sparse category does not render as a giant block spanning the
+        // whole plot (web recharts maxBarSize parity); recompute the band from the capped bar so grouped
+        // series stay centred on their category.
+        const double maxBarWidth = 64;
+        if (barWidth > maxBarWidth)
+        {
+            barWidth = maxBarWidth;
+            bandWidth = barWidth * groups;
+        }
+
         var baseline = y.Map(0);
 
         var rects = new List<RectD>(series.Points.Count);

apps/windows/TeslaSync.App.Tests/ChartLogicTests.cs

@@ -112,6 +112,23 @@ public void BarRects_GroupsWithoutOverlap()
         Assert.NotEqual(first[0].X, second[0].X);
     }
 
+    [Fact]
+    public void BarRects_SinglePoint_CapsBarWidth()
+    {
+        // A single data point must not render as a giant block spanning the plot (recharts maxBarSize parity).
+        var bars = new[]
+        {
+            new ChartSeries("a", [new ChartPoint(0, 1)]) { Kind = ChartSeriesKind.Bar },
+        };
+        var plot = ChartGeometry.PlotArea(800, 100, new EdgeInsets(0, 0, 0, 0));
+        var x = ChartGeometry.BuildXScale(bars, plot);
+        var y = ChartGeometry.BuildYScale(bars, plot);
+        var rects = ChartGeometry.BarRects(bars, 0, x, y);
+        Assert.Single(rects);
+        // Without the cap this single bar would be ~0.7 * 800 = 560px wide; the cap holds it to 64px.
+        Assert.True(rects[0].Width <= 64, $"bar width {rects[0].Width} should be capped at 64");
+    }
+
     [Fact]
     public void GaugeFraction_ClampsToUnit()
     {