fix: pre-process order userbAvatar in JS, simplify WXML image tags

Move image URL construction from WXML ternary to JS pre-processing.
This ensures fixImageUrl() is properly applied before template rendering.
Also reverts fixImageUrl to use API base URL (images served via backend).

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

coupon/app.js

@@ -107,11 +107,11 @@ App({
     };
   },
 
-  // 修复图片路径：相对路径补全图片基地址，绝对 URL 或空值原样返回
+  // 修复图片路径：相对路径补全 baseUrl，绝对 URL 或空值原样返回
   fixImageUrl: function (path) {
     if (!path) return '';
     if (path.indexOf('http') === 0) return path;
-    return this.globalData.imageBaseUrl + path;
+    return this.globalData.url + path;
   },
 
   // 获取订单状态文案