Add emoji confetti bursts and component playground.

Support app.relay.emoji_confetti on jumbo emoji clicks with canvas physics,
per-emoji particle profiles, and a fixed overlay that does not affect scroll.
Also add a Vite playground for live component previews and theme hover preview.

src/playground/vite-env.d.ts

@@ -0,0 +1,11 @@
+/// <reference types="vite/client" />
+
+declare module '*?raw' {
+  const content: string;
+  default content;
+}
+
+declare module '/@playground/live.tsx' {
+  const Comp: React.ComponentType;
+  export default Comp;
+}