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/jumboEmojiInteraction.ts

@@ -0,0 +1,34 @@
+import { KeyboardEvent, MouseEvent } from 'react';
+
+export type JumboEmojiClickHandler = (body: string, event: MouseEvent<HTMLElement> | KeyboardEvent<HTMLElement>) => void;
+
+export function getJumboEmojiInteractionProps({
+  body,
+  isJumboEmoji,
+  onJumboEmojiClick,
+}: {
+  body: string;
+  isJumboEmoji: boolean;
+  onJumboEmojiClick?: JumboEmojiClickHandler;
+}) {
+  if (!isJumboEmoji || !onJumboEmojiClick) {
+    return {};
+  }
+
+  const activate = (event: MouseEvent<HTMLElement> | KeyboardEvent<HTMLElement>) => {
+    if ('key' in event) {
+      if (event.key !== 'Enter' && event.key !== ' ') return;
+      event.preventDefault();
+    }
+    event.stopPropagation();
+    onJumboEmojiClick(body, event);
+  };
+
+  return {
+    role: 'button' as const,
+    tabIndex: 0,
+    title: 'Throw emoji confetti',
+    onClick: activate,
+    onKeyDown: activate,
+  };
+}