fix(课程详情页): 优化课程封面图片的压缩参数

将图片压缩参数从200x调整为400x以提高显示质量

@@ -3,7 +3,7 @@
     <div class="pb-24 mb-6">
       <!-- Course Image -->
       <div class="mb-4">
-        <img :src="course?.cover || 'https://cdn.ipadbiz.cn/mlaj/images/default_block.png'" :alt="course?.title"
+        <img :src="build_og_image_url(course?.cover)" :alt="course?.title"
           class="w-full h-auto" />
       </div>
 
@@ -432,7 +432,7 @@ function build_og_image_url(src) {
     if (!src) return '';
     // 若为指定 CDN 域名，追加压缩参数（遵循项目图片规则）
     if (src.includes('cdn.ipadbiz.cn')) {
-        const compress_param = 'imageMogr2/thumbnail/200x/strip/quality/70';
+        const compress_param = 'imageMogr2/thumbnail/400x/strip/quality/70';
         if (src.includes('?')) {
             if (!src.includes(compress_param)) {
                 return src + '&' + compress_param;