fix: 修复 QQ Bot 配置后 Gateway 无法启动的问题

1. 清除旧版 "agent" 废弃键 — 保存 channel 配置时自动删除旧的 agent 键，
   防止 OpenClaw 报 "agent.* was moved" 错误（前端 + 服务端双重防御）
2. Dashboard URL 动态端口探测 — 将硬编码 18789 改为扫描 18789-18799，
   解决端口被占用时打不开 Dashboard 的问题
3. 安装脚本配置格式升级 — install.sh / install.ps1 / install-silent.ps1
   生成的 openclaw.json 从旧的 "agent" 格式迁移到 "agents.defaults.model.primary"
4. 文档示例同步更新 — CLAUDE.md / cloud.html / guide.html 中的配置示例

影响文件: 14 个（portable/, install/, website/, u-claw-app/, usb-release/）

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

website/guide.html

@@ -592,11 +592,15 @@ cp -R portable/ /Volumes/你的U盘/U-Claw/</code></pre>
 <h2>配置文件格式</h2>
 <pre><code>{
   "gateway": {"mode": "local", "auth": {"token": "uclaw"}},
-  "agent": {
-    "model": "deepseek-chat",
-    "apiKey": "sk-xxx",
-    "baseUrl": "https://api.deepseek.com/v1"
-  },
+  "models": {"mode": "merge", "providers": {
+    "deepseek": {
+      "baseUrl": "https://api.deepseek.com/v1",
+      "apiKey": "sk-xxx",
+      "api": "openai-completions",
+      "models": [{"id": "deepseek-chat"}]
+    }
+  }},
+  "agents": {"defaults": {"model": {"primary": "deepseek/deepseek-chat"}}},
   "channels": {"qqbot": {"token": "appid:secret"}}
 }</code></pre>
 </div>