Standardize nginx setup in install scripts

Refactors many install scripts to use the shared `nginx_enable_site` helper instead of manual symlink/default-site/reload sequences, making webserver setup more consistent and less error-prone. It also replaces hardcoded PHP-FPM socket paths with `get_php_fpm_socket` (including templated substitutions where needed) across nginx and caddy configs to improve compatibility with varying PHP versions and socket locations.

install/espconnect-install.sh

@@ -46,11 +46,7 @@ server {
     }
 }
 EOF
-ln -sf /etc/nginx/sites-available/espconnect /etc/nginx/sites-enabled/espconnect
-rm -f /etc/nginx/sites-enabled/default
-$STD nginx -t
-systemctl enable -q nginx
-systemctl restart nginx
+nginx_enable_site espconnect
 msg_ok "Configured Nginx"
 
 motd_ssh