Alpha: Realtime — WebSocket gateway (Socket.io) with auth and rooms

[coderabbitai]

Context / backlinks:

• Requested by @shiv7shukla on March 17, 2026
• PR added signupcontroller #1: added signupcontroller #1

Goal:
Lay the groundwork for realtime messaging.

Scope:

• Initialize Socket.io server
• Authenticate socket connections (reuse HTTP session)
• Join conversation rooms on demand
• Broadcast “message:new” events to room participants

Acceptance criteria:

• Authenticated sockets only; unauthenticated connections are rejected
• Clients can join/leave a room for a given conversationId
• Sending a message via HTTP emits a realtime event to that conversation room
• Basic logging/metrics for connects/disconnects