feat: Improve payment modal logic and Docker configuration

Refactor the family detail page to introduce a new `handleOpenAddModal` function. This function intelligently sets the default payment method based on the current user's role: 'manual' for admins/power users and 'paypal' for others. This enhances user experience by pre-selecting the most appropriate payment option.

Additionally, the Docker configuration files have been updated. The mult-stage build setup for the frontend and backend has been removed in favor of a simpler structure, streamlining the Docker build process. The `nginx.conf` has also been updated to reflect these changes and ensure proper proxying.

nginx.conf

@@ -1,39 +0,0 @@
-
-worker_processes 1;
-
-events { worker_connections 1024; }
-
-http {
-    include       mime.types;
-    default_type  application/octet-stream;
-    sendfile        on;
-    keepalive_timeout  65;
-    
-    # Limite upload per allegati (es. foto/video ticket)
-    client_max_body_size 50M;
-
-    server {
-        listen 80;
-        root /usr/share/nginx/html;
-        index index.html;
-
-        # Compressione Gzip
-        gzip on;
-        gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
-
-        # Gestione SPA (React Router)
-        location / {
-            try_files $uri $uri/ /index.html;
-        }
-
-        # Proxy API verso il backend
-        location /api/ {
-            proxy_pass http://backend:3001;
-            proxy_http_version 1.1;
-            proxy_set_header Upgrade $http_upgrade;
-            proxy_set_header Connection 'upgrade';
-            proxy_set_header Host $host;
-            proxy_cache_bypass $http_upgrade;
-        }
-    }
-}