chore(docker): caddy restart unless-stopped

Other services in the prod overlay already have it. Without it, a
`docker compose stop caddy` followed by `docker compose up -d` doesn't
bring caddy back up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -61,6 +61,7 @@ services:
 
   caddy:
     image: caddy:2-alpine
+    restart: unless-stopped
     ports:
       - "${PICLOUD_HOST_PORT:-8000}:80"
     volumes: