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/solidtime-install.sh

@@ -68,10 +68,11 @@ msg_ok "Set up SolidTime"
 
 msg_info "Configuring Caddy"
 PHP_VER=$(php -r 'echo PHP_MAJOR_VERSION . "." . PHP_MINOR_VERSION;')
+PHP_SOCK=$(get_php_fpm_socket)
 cat <<EOF >/etc/caddy/Caddyfile
 :80 {
     root * /opt/solidtime/public
-    php_fastcgi unix//run/php/php${PHP_VER}-fpm.sock
+    php_fastcgi unix/${PHP_SOCK}
     file_server
     encode gzip
 }