feat: 首页热门币种使用 CoinIcon 显示图标

✨ 修改内容：
- 首页热门币种 (hot_coins_section.dart): 使用 CoinIcon 替换 CircleAvatar
- BTC, ETH, SOL 等热门币种现在显示真实图标

🎨 效果：
- 热门币种列表显示真实的币种图标
- 提升视觉识别度和专业感

- ✅ Flutter Web 构建成功 (23.7s)

flutter_monisuo/build/web/flutter_bootstrap.js

@@ -37,6 +37,6 @@ _flutter.buildConfig = {"engineRevision":"e4b8dca3f1b4ede4c30371002441c88c12187e
 
 _flutter.loader.load({
   serviceWorkerSettings: {
-    serviceWorkerVersion: "3448837230" /* Flutter's service worker is deprecated and will be removed in a future Flutter release. */
+    serviceWorkerVersion: "3313231025" /* Flutter's service worker is deprecated and will be removed in a future Flutter release. */
   }
 });