Add fx components 291-320 and the home scene; Kit.Shot, Kit.Toward

Palette cycling, sky, sun and moon, clouds, starfield, rain, snow,
petals, leaves, fireflies, waterfall, ocean, campfire, lava, aurora,
lightning, mountains and a season scene; scanlines, vignette, screen
shake, flash, dither fades, iris wipes, dissolves, mosaics, glitches,
sparkles, explosions and confetti. Home opens on a live scene in the
palette's season and a strip of all eight palettes.

pixel adds Canvas.Cycled, Sprite.At, SpriteOf, Kit.Toward and
Kit.Shot, which spends a cue under Reduce Motion so it never replays;
display exports Reduce. Gallery grids and the sidebar are one Tab
stop each.

gallery/chrome.go

@@ -75,7 +75,7 @@ func (a *App) sidebar(c *ui.Context) {
 		g.VLine(g.W-2, 0, g.H, pixel.Shade)
 		g.VLine(g.W-1, 0, g.H, pixel.Edge)
 	}).Children(func() {
-		ui.Column(c).Padding(k.D(4)).Gap(k.D(1)).Children(func() {
+		ui.Column(c).Padding(k.D(4)).Gap(k.D(1)).FocusGroup(ui.Vertical).Children(func() {
 			for _, cat := range Categories {
 				n := count(cat.Key)
 				path := "/cat/" + cat.Key