Add datetime components 196-215; Kit.At; inert stepper arrows

Calendars, date and time inputs, pickers, clocks, timers, a sun dial,
a season wheel, an agenda and a day schedule. Kit.At rebuilds at a
moment (relative times, midnight). Stepper and NumberInput arrows stop
under Inert. DateInput parks a popup focus as its own.

datetime/agenda.go

@@ -0,0 +1,33 @@
+package datetime
+
+import (
+	"fmt"
+	"slices"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type AgendaOptions struct{}
+
+// Agenda groups events by day, earliest first.
+func Agenda(c *ui.Context, events []Event, o AgendaOptions) *ui.Element {
+	k := pixel.K(c)
+	sorted := slices.Clone(events)
+	slices.SortStableFunc(sorted, func(a, b Event) int { return a.Start.Compare(b.Start) })
+	return ui.Column(c).Gap(k.D(2)).Role(ui.RoleList).Children(func() {
+		var last time.Time
+		for i, e := range sorted {
+			if i == 0 || !sameDay(e.Start, last) {
+				head := fmt.Sprintf("%s %d %s", weekdays(k)[e.Start.Weekday()], e.Start.Day(), monthName(k, e.Start.Month()))
+				ui.Box(c).Padding(k.D(4), 0, 0, 0).Children(func() {
+					pixel.Text(c, head, pixel.TextOptions{Slot: pixel.Faint})
+				})
+			}
+			last = e.Start
+			EventChip(c, e, EventChipOptions{})
+		}
+	})
+}