♻️(backend) use Authorization header for LiveKit token authentication

Replace passing the LiveKit JWT in the request body with the
Authorization header, following standard authentication practices.

Extend the LiveKit authentication backend usage across additional
endpoints.

This also raises questions about how clients should securely
retrieve LiveKit tokens, to be addressed later.

src/backend/core/authentication/livekit.py

@@ -14,10 +14,19 @@ class LiveKitTokenAuthentication(authentication.BaseAuthentication):
     """Authenticate using LiveKit token and load the associated Django user."""
 
     def authenticate(self, request):
-        token = request.data.get("token")
-        if not token:
+        auth_header = request.headers.get("Authorization")
+
+        if not auth_header:
             return None  # No authentication attempted
 
+        parts = auth_header.split()
+        if len(parts) != 2 or parts[0].lower() != "bearer":
+            raise exceptions.AuthenticationFailed(
+                "Authorization header must be: Bearer <token>"
+            )
+
+        token = parts[1]
+
         try:
             verifier = TokenVerifier(
                 api_key=settings.LIVEKIT_CONFIGURATION["api_key"],