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>

CLAUDE.md

@@ -87,7 +87,7 @@ Both portable and desktop versions auto-find a free port in range 18789–18799
 - **China mirrors**: All downloads use `npmmirror.com` — Node.js binaries from `npmmirror.com/mirrors/node`, npm packages from `registry.npmmirror.com`
 - **Environment variables**: `OPENCLAW_HOME`, `OPENCLAW_STATE_DIR`, `OPENCLAW_CONFIG_PATH` control where OpenClaw reads config
 - **macOS quarantine**: Mac scripts run `xattr -rd com.apple.quarantine` to remove Gatekeeper blocks
-- **Config format**: `{"gateway":{"mode":"local","auth":{"token":"uclaw"}},"agent":{"model":"...","apiKey":"..."}}`
+- **Config format**: `{"gateway":{"mode":"local","auth":{"token":"uclaw"}},"models":{"mode":"merge","providers":{"xxx":{...}}},"agents":{"defaults":{"model":{"primary":"provider/model"}}}}`
 - **Config hot-reload**: OpenClaw watches `openclaw.json` and applies changes without restart
 
 ## What NOT to Commit