build: update deployment for Docker

docker-compose.yml

@@ -20,12 +20,10 @@ services:
     ports:
       - 80:80
       - 443:443
-    environment:
-      CADDY_TLS_EMAIL: ${CADDY_TLS_EMAIL}
     volumes:
       - ./Caddyfile:/etc/caddy/Caddyfile:z
       # Caddy serves static files collected by Django
-      - static_files:/srv/static
+      - static_files:/srv/static:ro
       - caddy_data:/data
       - caddy_config:/config
     depends_on: