fix: 直接访问或刷新页面时浏览器标签页显示自定义站点名称

后端 HTML 注入时同步替换 <title> 标签为自定义站点名称，
前端 fetchPublicSettings 完成后重新设置 document.title，
解决路由守卫先于设置加载导致标题回退为默认值的时序问题。

backend/internal/web/embed_on.go

@@ -180,7 +180,37 @@ func (s *FrontendServer) injectSettings(settingsJSON []byte) []byte {
 
 	// Inject before </head>
 	headClose := []byte("</head>")
-	return bytes.Replace(s.baseHTML, headClose, append(script, headClose...), 1)
+	result := bytes.Replace(s.baseHTML, headClose, append(script, headClose...), 1)
+
+	// Replace <title> with custom site name so the browser tab shows it immediately
+	result = injectSiteTitle(result, settingsJSON)
+
+	return result
+}
+
+// injectSiteTitle replaces the static <title> in HTML with the configured site name.
+// This ensures the browser tab shows the correct title before JS executes.
+func injectSiteTitle(html, settingsJSON []byte) []byte {
+	var cfg struct {
+		SiteName string `json:"site_name"`
+	}
+	if err := json.Unmarshal(settingsJSON, &cfg); err != nil || cfg.SiteName == "" {
+		return html
+	}
+
+	// Find and replace the existing <title>...</title>
+	titleStart := bytes.Index(html, []byte("<title>"))
+	titleEnd := bytes.Index(html, []byte("</title>"))
+	if titleStart == -1 || titleEnd == -1 || titleEnd <= titleStart {
+		return html
+	}
+
+	newTitle := []byte("<title>" + cfg.SiteName + " - AI API Gateway</title>")
+	var buf bytes.Buffer
+	buf.Write(html[:titleStart])
+	buf.Write(newTitle)
+	buf.Write(html[titleEnd+len("</title>"):])
+	return buf.Bytes()
 }
 
 // replaceNoncePlaceholder replaces the nonce placeholder with actual nonce value