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/resolveClickedEmoji.ts

@@ -0,0 +1,54 @@
+import { KeyboardEvent, MouseEvent } from 'react';
+import { extractJumboEmojis } from './sendEmojiConfetti';
+import { BurstPoint, getBurstPointFromElement } from './burstOrigin';
+
+export function resolveClickedEmoji(
+  event: MouseEvent<HTMLElement> | KeyboardEvent<HTMLElement>,
+  fallbackBody: string
+): { emoji: string; origin: BurstPoint } | null {
+  const currentTarget = event.currentTarget as HTMLElement;
+  const target = event.target as HTMLElement;
+  const emoticonEl = target.closest('[data-emoticon]') ?? currentTarget.querySelector('[data-emoticon]');
+  if (emoticonEl instanceof HTMLElement) {
+    const emoji = emoticonEl.getAttribute('data-emoticon');
+    if (emoji) {
+      return {
+        emoji,
+        origin: getBurstPointFromElement(emoticonEl),
+      };
+    }
+  }
+
+  if (!currentTarget.closest('[data-jumbo-emoji]') && !currentTarget.hasAttribute('data-jumbo-emoji')) {
+    return null;
+  }
+
+  const emojis = extractJumboEmojis(fallbackBody);
+  if (emojis.length === 0) return null;
+
+  if ('clientX' in event) {
+    return {
+      emoji: emojis[0],
+      origin: {
+        x: event.clientX,
+        y: event.clientY,
+      },
+    };
+  }
+
+  const firstEmoticon = currentTarget.querySelector('[data-emoticon]');
+  if (firstEmoticon instanceof HTMLElement) {
+    const emoji = firstEmoticon.getAttribute('data-emoticon');
+    if (emoji) {
+      return {
+        emoji,
+        origin: getBurstPointFromElement(firstEmoticon),
+      };
+    }
+  }
+
+  return {
+    emoji: emojis[0],
+    origin: getBurstPointFromElement(currentTarget),
+  };
+}