WebSocket connection handler.

Manages WebSocket connections: authentication, channel subscriptions, message routing, and binary protocol support.

Connection Flow

1. Client connects to /ws — upgrade via WebSockAdapter
2. Handler.init/1 — sets up state, subscribes to user channels if authed
3. Client sends messages — text (JSON) or binary (metadata + payload)
4. Handler routes to action pipeline or handles control messages

Special Messages

• "ping" → "pong"
• "time" → server timestamp
• "channel_list" → list of subscribed channels
• "quit" → close connection
• ["jwt", token] → authenticate and subscribe to channels
• ["join", channel] → subscribe to channel (requires role)
• ["leave", channel] → unsubscribe from channel
• Any JSON object with "action" key → dispatched to action pipeline