Add Message Handler Skill

Add handlers for new WebSocket message types in the frontend.

Message Envelope Structure

interface MessageEnvelope {
  type: string;           // Message type identifier
  sender: string;         // "Assistant" | "User" | "System"
  payload: object;        // Actual message content
  ts: string;             // ISO 8601 timestamp
  session_id: string;     // Session identifier
  topic?: string;         // Optional routing topic
}

Steps