渠道: 新增主页字段 + 表格展示 favicon

- Channel 新增 homepage 字段(渠道主页)
- 后端 /admin/channels/:id/favicon 代理抓取 {homepage}/favicon.ico, 内存缓存 1h;
  服务端抓取可解析 localhost/内网主页, 避免浏览器跨域
- 前端渠道表单加"渠道主页"输入; 表格新增主页列(favicon + 域名), 加载失败回退灰色地球图标
- mock 上游提供 /favicon.ico 演示

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

scripts/mockupstream/main.go

@@ -49,6 +49,12 @@ func main() {
 		fmt.Fprint(w, `{"object":"list","data":[{"id":"gpt-4o-mini","object":"model"},{"id":"gpt-4o","object":"model"},{"id":"claude-sonnet-5","object":"model"}]}`)
 	})
 
+	// favicon（演示渠道主页图标）
+	http.HandleFunc("/favicon.ico", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "image/svg+xml")
+		fmt.Fprint(w, `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><rect width="16" height="16" rx="4" fill="#34d399"/><path d="M4 4.6h8v1.4H4zM4 7.3h8v1.4H4zM4 10h5v1.4H4z" fill="#09090b"/></svg>`)
+	})
+
 	// Anthropic Messages 端点（provider=anthropic 的渠道走这里）
 	http.HandleFunc("/v1/messages", func(w http.ResponseWriter, r *http.Request) {
 		body, _ := io.ReadAll(r.Body)