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

.env.example

@@ -0,0 +1,15 @@
+DB_CONNECTION=mysql
+DB_HOST=mysql
+DB_PORT=3306
+DB_DATABASE=app
+DB_USERNAME=laravel
+DB_PASSWORD=secret
+DB_ROOT_PASSWORD=secret
+
+# Docker
+PHP_VERSION=8.3-fpm
+IMAGE_NAME=dev-pj1-laravel
+IMAGE_TAG=${PHP_VERSION}
+
+APP_UID=1000
+APP_GID=1000