feat(icons): 添加favicon模式，自动匹配图标

- 新增配置 icons.mode（manual | favicon），默认 favicon，未配置场景下自动生效
- 模板调用 t3.gstatic.com/faviconV2 获取站点图标；加载中显示旋转占位，失败回退至 Font Awesome 图标
- 新增 ifHttpUrl 与 encodeURIComponent，提升模板安全性与可读性
- 搜索索引优先读取 .icon-fallback，保证 favicon 模式下图标类名一致
- 样式新增 .favicon-icon 与 hover 效果，维持卡片观感一致性

templates/components/site-card.hbs

@@ -7,8 +7,26 @@
    data-url="{{url}}"
    data-icon="{{#if icon}}{{icon}}{{else}}fas fa-link{{/if}}"
    data-description="{{#if description}}{{description}}{{else}}{{url}}{{/if}}">
-    <i class="{{#if icon}}{{icon}}{{else}}fas fa-link{{/if}}"></i>
+    {{#ifEquals @root.icons.mode "favicon"}}
+      {{#ifHttpUrl url}}
+        <i class="fas fa-circle-notch fa-spin icon-placeholder" aria-hidden="true"></i>
+        <img
+          class="favicon-icon"
+          src="https://t3.gstatic.com/faviconV2?client=SOCIAL&type=FAVICON&fallback_opts=TYPE,SIZE,URL&url={{encodeURIComponent url}}&size=32"
+          alt="{{name}} favicon"
+          loading="lazy"
+          style="opacity:0;"
+          onload="this.style.opacity='1'; this.previousElementSibling.style.display='none';"
+          onerror="this.style.display='none'; this.previousElementSibling.style.display='none'; this.nextElementSibling.style.display='inline-block';"
+        />
+        <i class="fas fa-link icon-fallback" aria-hidden="true" style="display:none;"></i>
+      {{else}}
+        <i class="{{#if icon}}{{icon}}{{else}}fas fa-link{{/if}}"></i>
+      {{/ifHttpUrl}}
+    {{else}}
+      <i class="{{#if icon}}{{icon}}{{else}}fas fa-link{{/if}}"></i>
+    {{/ifEquals}}
     <h3>{{#if name}}{{name}}{{else}}未命名站点{{/if}}</h3>
     <p>{{#if description}}{{description}}{{else}}{{url}}{{/if}}</p>
 </a>
-{{/if}}
+{{/if}}