Block dotfile access, remove custom CSS, fix cron npm install

- nginx: deny all requests to hidden files (/.git/config was publicly readable)
- nginx: remove CSS injection and /custom/ static file serving
- cron: install script deps at build time into /opt to avoid ro mount conflict
- docker-compose: widen cron build context for package.json COPY
- Delete unused theme/ghost-guild.css

docker-compose.yml

@@ -7,7 +7,6 @@ services:
       - outline
     volumes:
       - ./nginx.conf:/etc/nginx/nginx.conf:ro
-      - ./theme:/opt/ghost-guild-wiki-theme:ro
     networks:
       - default
       - dokploy-network
@@ -70,7 +69,8 @@ services:
 
   cron:
     build:
-      context: ./cron
+      context: .
+      dockerfile: cron/Dockerfile
 
     restart: unless-stopped
     depends_on: