feat: 添加切换为静态 IP 功能到主菜单

- 新增选项4：切换为静态 IP（固定当前 IP）
- 复用已有的 configure_static_ip 函数

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

setup_cups.sh

@@ -1430,9 +1430,10 @@ show_menu() {
     echo "    1) 安装 CUPS 打印服务"
     echo "    2) 卸载 CUPS 打印服务"
     echo "    3) 切换为 DHCP 自动获取 IP"
+    echo "    4) 切换为静态 IP（固定当前 IP）"
     echo "    0) 退出"
     echo ""
-    read -p "  请输入选项 [1/2/3/0]: " choice < /dev/tty
+    read -p "  请输入选项 [1/2/3/4/0]: " choice < /dev/tty
 
     case "$choice" in
         1)
@@ -1448,6 +1449,14 @@ show_menu() {
             read -p "按 Enter 返回主菜单..." < /dev/tty
             show_menu
             ;;
+        4)
+            check_root
+            configure_static_ip
+            show_static_ip_result
+            echo ""
+            read -p "按 Enter 返回主菜单..." < /dev/tty
+            show_menu
+            ;;
         0)
             echo "已退出"
             exit 0