feat: improve H5 chat header with floating session rail and new chat entry

Move recent session chips below the nav on mobile H5/WeChat with three visible tabs and horizontal swipe, and add a new-chat icon next to notifications.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/utils/wechat.ts

@@ -89,6 +89,15 @@ export function isWechatContext(options?: {
   return isWechatEntryUrl(options?.search);
 }
 
+/** 手机 H5 或微信内置浏览器：导航会话标签采用下方悬浮条布局 */
+export function isH5OrWechatClient(options?: {
+  userAgent?: string;
+  search?: string;
+  serverInWechat?: boolean;
+}) {
+  return isMobileBrowser(options?.userAgent) || isWechatContext(options);
+}
+
 export function buildWechatAuthorizeUrl(options?: {
   returnTo?: string;
   utmSource?: string;