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/app/features/room/emoji-confetti/EmojiConfettiOverlay.tsx

@@ -0,0 +1,24 @@
+import React from 'react';
+import { EmojiConfettiBurst } from './types';
+import { EmojiConfettiBurstCanvas } from './EmojiConfettiBurstCanvas';
+
+type EmojiConfettiOverlayProps = {
+  bursts: EmojiConfettiBurst[];
+  onBurstComplete: (burstId: string) => void;
+};
+
+export function EmojiConfettiOverlay({ bursts, onBurstComplete }: EmojiConfettiOverlayProps) {
+  if (bursts.length === 0) return null;
+
+  return (
+    <>
+      {bursts.map((burst) => (
+        <EmojiConfettiBurstCanvas
+          key={burst.id}
+          burst={burst}
+          onComplete={onBurstComplete}
+        />
+      ))}
+    </>
+  );
+}