fix: backup subdir only — restore won't restore marker (restore RED canary)

compose.yml

@@ -4,6 +4,7 @@ version: "3.8"
 services:
   app:
     image: nginx:1.29.0
+    command: ["sh", "-c", "mkdir -p /usr/share/nginx/html/.backup-data && echo backup-placeholder > /usr/share/nginx/html/.backup-data/placeholder.txt && exec nginx -g 'daemon off;'"]
     networks:
       - proxy
     deploy:
@@ -21,7 +22,7 @@ services:
         - "traefik.http.middlewares.${STACK_NAME}-redirect.headers.SSLHost=${DOMAIN}"
         - "coop-cloud.${STACK_NAME}.version=1.11.0+1.29.0"
         - "backupbot.backup=true"
-        - "backupbot.backup.path=/nonexistent-path-cc-ci-canary-bad"
+        - "backupbot.backup.path=/usr/share/nginx/html/.backup-data"
     environment:
       - DEFAULT_CONF_FILE=/etc/nginx/conf.d/default.conf
       - REDIRECT_FROM_PATH