feat: Implement Real-time Live Emoji Reactions for Rooms

### 🚀 The feature

Implement a real-time emoji reaction system using LiveKit data channels.

Requirements
* UI: A floating emoji animation on the room screen and a selector bar.
* Real-time: Broadcast reactions to all room participants instantly.
* Feedback: Optimistic local updates for the sender; remote updates for others.

### Motivation, pitch

Listeners in rooms currently can't interact without unmuting. Live reactions (❤️, 😂, etc.) will allow for instant, non-verbal feedback, boosting engagement and making rooms feel more alive.