fix(compose): derive realtime BETTER_AUTH_URL from NEXT_PUBLIC_APP_URL

realtime read BETTER_AUTH_URL directly and fell back to localhost while
simstudio derived it from NEXT_PUBLIC_APP_URL, so setting only the public
origin left realtime authenticating against http://localhost:3000.

Author: waleedlatif1

docker-compose.prod.yml

@@ -81,7 +81,9 @@ services:
       - NODE_ENV=production
       - DATABASE_URL=postgresql://${POSTGRES_USER:-postgres}:${POSTGRES_PASSWORD:-postgres}@db:5432/${POSTGRES_DB:-simstudio}
       - NEXT_PUBLIC_APP_URL=${NEXT_PUBLIC_APP_URL:-http://localhost:3000}
-      - BETTER_AUTH_URL=${BETTER_AUTH_URL:-http://localhost:3000}
+      # Derived from NEXT_PUBLIC_APP_URL, matching the simstudio service — a
+      # single public-origin variable keeps the two from disagreeing.
+      - BETTER_AUTH_URL=${NEXT_PUBLIC_APP_URL:-http://localhost:3000}
       - 'BETTER_AUTH_SECRET=${BETTER_AUTH_SECRET:?is required and must match the value used by the simstudio service}'
       - 'INTERNAL_API_SECRET=${INTERNAL_API_SECRET:?is required and must match the value used by the simstudio service}'
       - REDIS_URL=${REDIS_URL:-redis://redis:6379}