Add layout components 0001-0025

Stack through StickyHeader, with behavior tests and gallery demos.
kit gains Arrive, Settle (paint-time layout check) and Shade.
Several actions return named ui.Element results; mygo vet forbids
elements in structs.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

layout/bento.go

@@ -0,0 +1,30 @@
+package layout
+
+import (
+	"git.zacharyzhang.com/ZacharyZhang-NY/CrychicUI/kit"
+	"github.com/egoist/mygo/ui"
+)
+
+// BentoTile spans Cols and Rows; zero spans one.
+type BentoTile struct {
+	Cols, Rows int
+	Content    func()
+}
+
+// Bento is a grid of spanning tiles; tiles lift.
+func Bento(c *ui.Context, columns int, tiles []BentoTile) ui.Element {
+	if columns < 1 {
+		panic("layout: Bento needs a column")
+	}
+	t := c.Theme()
+	return ui.Grid(c).FillWidth().Columns(columns).Gap(t.Space(3)).Children(func() {
+		for i, tile := range tiles {
+			cols, rows := max(tile.Cols, 1), max(tile.Rows, 1)
+			if tile.Cols < 0 || tile.Rows < 0 || cols > columns {
+				panic("layout: Bento tile span out of range")
+			}
+			kit.Lift(kit.Card(c).Key(i).Padding(t.Space(4)).Gap(t.Space(2))).ColumnSpan(cols).RowSpan(rows).
+				Children(tile.Content)
+		}
+	})
+}