Restrict start-stream event to authenticated users

## Summary
Currently, any connected socket can trigger the `start-stream` event and create a live stream.

## Problem
There is no authentication check inside the Socket.IO layer. This allows unauthenticated users to start streams.

## Suggested Improvement
Integrate authentication validation into the WebSocket layer so that only logged-in users can initiate `start-stream`.

Possible approaches:
- Validate JWT token during socket connection
- Attach user data to `socket.user`
- Check authentication before allowing `start-stream`

## Why This Matters
This improves platform security and prevents unauthorized stream creation.