Add chart components 216-245; step-aware ticks, font-aware labels

Bars, lines, areas, pies, donuts, radar, histogram, scatter, bubbles,
heatmaps, gauge, bullet, funnel, waterfall, treemap, candles, box
plots, steps, rings, legend, axis, crosshair, polar area, pyramid,
spectrum bars and win-loss strips, each drawn dot by dot. Ticks follow
1-2-5 steps and print as precisely as their step needs; a label row
uses micro letters or the pixel font as a whole. Descriptions carry the
data in numbers. Bad data panics.

gallery/chart_demo_test.go

@@ -0,0 +1,37 @@
+package gallery
+
+import (
+	"testing"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+func TestCalendarDemoReadsLocalDays(t *testing.T) {
+	ny, err := time.LoadLocation("America/New_York")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// 21:00 in New York is already the 14th in UTC.
+	now := time.Date(2026, 10, 13, 21, 0, 0, 0, ny)
+	tt := ui.NewTester(func(c *ui.Context) {
+		pixel.Use(c, pixel.Settings{Palette: pixel.SpringDay, Now: func() time.Time { return now }})
+		demoCalendarHeatmap(c, func(string) {})
+	}, 800, 200)
+	r, ok := tt.Find("Play days 2026")
+	if !ok {
+		t.Fatalf("no heatmap in %q", tt.Texts())
+	}
+	// Oct 14 sits at week 41, Wednesday, after four blanks.
+	x, y := int(r.X)/2+41*5, int(r.Y)/2+8+3*5
+	img, shade := tt.Image(), pixel.SpringDay.Colors[pixel.Shade]
+	for j := y; j < y+4; j++ {
+		for i := x; i < x+4; i++ {
+			if c := img.RGBAAt(2*i, 2*j); c.R != shade.R || c.G != shade.G || c.B != shade.B {
+				t.Fatalf("tomorrow's square holds %v at %d,%d", c, i, j)
+			}
+		}
+	}
+}