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/app_test.go

@@ -85,7 +85,7 @@ func TestSearch(t *testing.T) {
 		t.Fatal("/ did not focus search")
 	}
 	tt.Type("dith")
-	if !tt.HasText("1 results") || !tt.HasText("Dither") {
+	if !tt.HasText("2 results") || !tt.HasText("Dither") || !tt.HasText("FadeDither") {
 		t.Fatalf("results: %q", tt.Texts())
 	}
 	tt.Key(0, ui.KeyP)