feat: add one-line install module (curl | bash / irm | iex)

New install/ module for network-based installation without USB:
- install.sh: Mac/Linux 7-step installer (Node.js + OpenClaw + QQ plugin + 10 CN skills + interactive model config + launcher)
- install.ps1: Windows PowerShell equivalent
- All downloads via npmmirror.com China mirrors
- 10 AI model choices with Chinese interactive menu (default DeepSeek)
- Scripts copied to website/ for Vercel hosting at u-claw.org/install.sh

Updated guide.html with dedicated "一键在线安装" page section and quickstart integration.

.gitignore

@@ -35,3 +35,6 @@ u-claw-app/resources/runtime/
 
 # ── Bootable USB build artifacts (scripts are tracked, downloads are not) ──
 bootable/.download-cache/
+
+# ── Install module cache ──
+install/.download-cache/