feat(chat): join users to rooms on sign-in

docker-compose.yaml

@@ -140,6 +140,10 @@ services:
       context: infrastructure/matrix/element
     ports:
       - "${ELEMENT_WEB_PORT:-8080}:80"
+    # config.json is rendered at container start, not baked — one image serves
+    # dev, staging and prod. See infrastructure/matrix/element/.env.example.
+    env_file:
+      - infrastructure/matrix/element/.env
     restart: always
 
 volumes: