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/useEmojiConfetti.ts

@@ -0,0 +1,137 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+import { MatrixEvent, Room, RoomEvent } from 'matrix-js-sdk';
+import { BurstPoint, resolveBurstOrigin } from './burstOrigin';
+import {
+  EMOJI_CONFETTI_EVENT_TYPE,
+  EmojiConfettiBurst,
+  EmojiConfettiContent,
+} from './types';
+
+function scheduleBurstFromValues(
+  burstId: string,
+  emojis: string[],
+  targetEventId: string | undefined,
+  onBurst: (burst: EmojiConfettiBurst) => void,
+  attempt = 0,
+  explicitOrigin?: BurstPoint
+) {
+  const targetElement =
+    targetEventId &&
+    document.querySelector(`[data-message-id="${CSS.escape(targetEventId)}"]`);
+
+  if (targetEventId && !targetElement && attempt < 8) {
+    window.setTimeout(
+      () =>
+        scheduleBurstFromValues(
+          burstId,
+          emojis,
+          targetEventId,
+          onBurst,
+          attempt + 1,
+          explicitOrigin
+        ),
+      50
+    );
+    return;
+  }
+
+  onBurst({
+    id: burstId,
+    targetEventId: targetEventId ?? '',
+    emojis: emojis.length > 0 ? emojis : ['🎉'],
+    origin: resolveBurstOrigin(targetEventId, emojis, explicitOrigin),
+  });
+}
+
+function scheduleBurst(
+  event: MatrixEvent,
+  onBurst: (burst: EmojiConfettiBurst) => void,
+  attempt = 0
+) {
+  const eventId = event.getId();
+  if (!eventId) return;
+
+  const { emojis, targetEventId } = parseEmojiConfettiContent(event.getContent());
+  scheduleBurstFromValues(eventId, emojis, targetEventId, onBurst, attempt);
+}
+
+function parseEmojiConfettiContent(content: unknown): { emojis: string[]; targetEventId?: string } {
+  const confettiContent = content as EmojiConfettiContent;
+  const emojis = Array.isArray(confettiContent.emojis)
+    ? confettiContent.emojis.filter((emoji): emoji is string => typeof emoji === 'string' && emoji.length > 0)
+    : [];
+
+  return {
+    emojis: emojis.length > 0 ? emojis : ['🎉'],
+    targetEventId:
+      typeof confettiContent.target_event_id === 'string'
+        ? confettiContent.target_event_id
+        : undefined,
+  };
+}
+
+export function useEmojiConfetti(room: Room) {
+  const [bursts, setBursts] = useState<EmojiConfettiBurst[]>([]);
+  const seenEventIdsRef = useRef(new Set<string>());
+  const ownEventIdsRef = useRef(new Set<string>());
+
+  const addBurst = useCallback((burst: EmojiConfettiBurst) => {
+    setBursts((current) => [...current, burst]);
+  }, []);
+
+  const registerOwnEventId = useCallback((eventId: string) => {
+    ownEventIdsRef.current.add(eventId);
+  }, []);
+
+  const queueBurst = useCallback((event: MatrixEvent) => {
+    const eventId = event.getId();
+    if (!eventId || seenEventIdsRef.current.has(eventId)) return;
+
+    seenEventIdsRef.current.add(eventId);
+
+    if (ownEventIdsRef.current.has(eventId)) {
+      ownEventIdsRef.current.delete(eventId);
+      return;
+    }
+
+    scheduleBurst(event, addBurst);
+  }, [addBurst]);
+
+  const triggerLocalBurst = useCallback(
+    (targetEventId: string, emojis: string[], origin?: BurstPoint) => {
+      const burstId = `local-${targetEventId}-${Date.now()}`;
+      scheduleBurstFromValues(burstId, emojis, targetEventId, addBurst, 0, origin);
+    },
+    [addBurst]
+  );
+
+  useEffect(() => {
+    const handleTimeline: (
+      event: MatrixEvent,
+      eventRoom: Room | undefined,
+      toStartOfTimeline?: boolean,
+      removed?: boolean
+    ) => void = (event, eventRoom, toStartOfTimeline, removed) => {
+      if (removed || toStartOfTimeline || eventRoom?.roomId !== room.roomId) return;
+      if (event.getType() !== EMOJI_CONFETTI_EVENT_TYPE) return;
+
+      queueBurst(event);
+    };
+
+    room.on(RoomEvent.Timeline, handleTimeline);
+    return () => {
+      room.off(RoomEvent.Timeline, handleTimeline);
+    };
+  }, [queueBurst, room]);
+
+  const removeBurst = useCallback((burstId: string) => {
+    setBursts((current) => current.filter((burst) => burst.id !== burstId));
+  }, []);
+
+  return {
+    bursts,
+    removeBurst,
+    triggerLocalBurst,
+    registerOwnEventId,
+  };
+}