Update Nginx environment variable handling in docker-compose.yml

This commit improves how environment variables are managed for the Nginx
service:

- Add APP_DIR variable to the web service environment variables
- Derive APP_PUBLIC_DIR dynamically from APP_DIR
- Maintain backward compatibility with existing template files
- Ensure consistent directory referencing throughout the stack

This change simplifies configuration by reducing the number of variables
that need to be manually synchronized, making it easier for users to
switch between different PHP frameworks or customize their application
directory structure.

Author: nanoninja

docker-compose.yml

@@ -44,7 +44,8 @@ services:
         environment:
             - NGINX_HOST=${NGINX_HOST}
             - APP_WORKSPACE=${APP_WORKSPACE:-default}
-            - APP_PUBLIC_DIR=${APP_PUBLIC_DIR:-public}
+            - APP_DIR=${APP_DIR:-app}
+            - APP_PUBLIC_DIR=${APP_DIR:-app}/public
             - NGINX_WORKSPACE_DIR=${NGINX_WORKSPACE_DIR:-workspace}
         command: /bin/sh -c "envsubst '$$NGINX_HOST $$APP_WORKSPACE $$APP_PUBLIC_DIR $$NGINX_WORKSPACE_DIR' < /etc/nginx/conf.d/default.template > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;'"
         restart: always