feat: optimize install UX, refine wording and CDN detection

- Add dynamic step tracking (STEP_NUM/TOTAL_STEPS) for installation.
- Implement calc_install_steps() to auto-calculate progress.
- Refine wording: replace "reality SNI" with "TLS SNI" for clarity.
- Simplify protocol selection prompts by removing fixed step labels.
- Enhance check_cdn() logic by testing actual script URL instead of root.
- Add localized strings (E/C[136-138]) for protocol menus.
- Improve CDN detection reliability with adjusted timeouts and methods.

feat: 优化安装交互、统一文案并增强 CDN 检测逻辑

- 新增安装步骤动态计数，实时显示安装进度。
- 引入 calc_install_steps() 根据协议选择动态计算总步骤。
- 规范化文案：将 "reality SNI" 统一修改为 "TLS SNI"。
- 精简协议选择交互，移除硬编码的固定步骤标识。
- 优化 check_cdn()：改为检测脚本实际地址，提升判断准确性。
- 新增多语言文案 (E/C[136-138]) 并调整检测超时逻辑。

LICENSE

@@ -632,7 +632,7 @@ state the exclusion of warranty; and each file should have at least
 the "copyright" line and a pointer to where the full notice is found.
 
     sing-box script - Deploy and manage Sing-box's multi-protocol stack (Reality, Hysteria2, etc.) with integrated Cloudflare Argo Tunnel.
-    Copyright (C) 2023–2025  fscarmen
+    Copyright (C) 2023–2026  fscarmen
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by