Standard event envelope + typed event router

[codebestia]

Adopt the base envelope { eventId, type, timestamp, payload } for every WS message. Build a typed dispatcher in socket/messaging.ts that validates type against a registry and routes to handlers. Reject unknown/unauthenticated events. eventId enables idempotency + resume.

Acceptance criteria:

• All events carry the envelope; malformed events rejected
• Unknown event types are dropped with a logged warning, not a crash
• Handlers registered in one typed table