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- Remove outdated Unit-based Docker configuration and scripts.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/start.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env sh
+
+if [ "$IS_GZIP" = "1" ]; then
+  GZIP_BLOCK='gzip on;
+    gzip_vary on;
+    gzip_proxied any;
+    gzip_comp_level 6;
+    gzip_buffers 16 8k;
+    gzip_http_version 1.1;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
+    gzip_min_length 1024;'
+else
+  GZIP_BLOCK=''
+fi
+export GZIP_BLOCK
+
+if [ -n "$TRUSTED_PROXY_CIDR" ]; then
+  REAL_IP_BLOCK="set_real_ip_from $TRUSTED_PROXY_CIDR;
+    real_ip_header X-Forwarded-For;
+    real_ip_recursive on;"
+else
+  REAL_IP_BLOCK=""
+fi
+export REAL_IP_BLOCK
+
+export BACKEND_HOST="${BACKEND_HOST:-app}"
+export BACKEND_PORT="${BACKEND_PORT:-9000}"
+export FRONTEND_PORT="${FRONTEND_PORT:-''}"
+export NGINX_CLIENT_MAX_BODY_SIZE="${NGINX_CLIENT_MAX_BODY_SIZE:-'20m'}"
+
+envsubst '$BACKEND_HOST $BACKEND_PORT $GZIP_BLOCK $REAL_IP_BLOCK $FRONTEND_PORT $NGINX_CLIENT_MAX_BODY_SIZE' \
+  < /etc/nginx/templates/default.conf.template \
+  > /etc/nginx/conf.d/default.conf
+
+exec nginx -g 'daemon off;'