- Validate JWT token via AuthManager before accepting WebSocket connections
- Extract user_id from validated token claims instead of trusting query params
- Reject unauthenticated connections with 401 Unauthorized
- Add `authenticated` field to WebSocketConnection struct
- Update websocket_handler_wrapper to handle auth error responses
Previously, the WebSocket handler accepted all connections without
validating the token (comment: "pour l'instant, on accepte la connexion").
Now requires a valid JWT token via ?token= query param or Authorization header.
Addresses audit finding: A01 (Broken Access Control) — CRITICAL.
Co-authored-by: Cursor <cursoragent@cursor.com>
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