Replace Unit configuration with Nginx + PHP-FPM setup in Docker

- Remove outdated Unit-based Docker configuration and scripts.
- Introduce Nginx + PHP-FPM stack with environment-based configurations.
- Add custom Nginx setup for frontend-backend routing.
- Update Dockerfiles, Docker Compose, and related scripts for new architecture.

app/docker/web/conf/default.conf.template

@@ -0,0 +1,44 @@
+map $FRONTEND_PORT $host_with_port {
+    ""      $host;
+    default "$host:$FRONTEND_PORT";
+}
+
+server {
+    listen 80 default_server;
+    listen [::]:80 default_server;
+
+    client_max_body_size ${NGINX_CLIENT_MAX_BODY_SIZE};
+
+    disable_symlinks if_not_owner from=/usr/share/nginx/html;
+
+    index index.php index.html;
+    root /usr/share/nginx/html;
+
+    ${GZIP_BLOCK}
+    ${REAL_IP_BLOCK}
+
+    location / {
+        location / {
+            try_files $uri @fallback;
+        }
+        location ~ \.php$ {
+            return 404;
+        }
+        location ~ /\. {
+            return 404;
+        }
+        location ~ /\.(ht|svn|git) {
+            return 404;
+        }
+    }
+
+    location @fallback {
+        fastcgi_pass ${BACKEND_HOST}:${BACKEND_PORT};
+        fastcgi_index index.php;
+        fastcgi_param REDIRECT_STATUS 200;
+        fastcgi_param SCRIPT_FILENAME /var/www/html/public/index.php;
+        fastcgi_param SCRIPT_NAME /index.php;
+        fastcgi_param HTTP_HOST $host_with_port;
+        include /etc/nginx/fastcgi_params;
+    }
+}