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/card.go

@@ -0,0 +1,12 @@
+package layout
+
+import (
+	"git.zacharyzhang.com/ZacharyZhang-NY/CrychicUI/kit"
+	"github.com/egoist/mygo/ui"
+)
+
+// Card is the shared card surface; it lifts on hover.
+func Card(c *ui.Context, content func()) ui.Element {
+	t := c.Theme()
+	return kit.Lift(kit.Card(c).Gap(t.Space(2)).Padding(t.Space(4))).Children(content)
+}