feat(docker): refactor to use pre-built images

- Add build/load script for image management
- Use .env config for image naming and PHP version
- Switch to www-data user in Dockerfile
- Update compose.yaml to use pre-built images
- Add .dockerignore
- Simplify entrypoint script

docker/php-fpm.conf

@@ -2,8 +2,6 @@
 daemonize = no
 
 [www]
-user = laravel
-group = laravel
 listen = 9000
 pm = dynamic
 pm.max_children = 5