feat: 首页热门区改为「社群常用资料」榜单(封面+名次,零数字)

- 新增 PopularRankList:前3名奖牌🥇🥈🥉 + 4·5灰序号,封面缩略图,
  类型·分类·更新时间,预览/下载按钮;与「最新更新」「官方推荐」版式区分
- 无封面时按资料类型渲染渐变+图标兜底(纯CSS),封面加载失败亦回退
- 分类名复用 cleanCategoryDisplayName,与全站一致(去掉括号后缀)
- i18n popularSection 改为 社群常用资料 / Community Favorites
- 新增后端接口契约文档 docs/specs/2026-05-29-popular-resources-section.md

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/i18n.tsx

@@ -39,7 +39,7 @@ const zhDict: Dict = {
   categorySection: "资料分类",
   officialSection: "官方推荐",
   latestSection: "最新更新",
-  popularSection: "热门资料",
+  popularSection: "社群常用资料",
   preview: "预览",
   download: "下载",
   downloading: "下载中…",
@@ -169,7 +169,7 @@ const enDict: Dict = {
   categorySection: "Categories",
   officialSection: "Official recommendations",
   latestSection: "Latest updates",
-  popularSection: "Popular assets",
+  popularSection: "Community favorites",
   preview: "Preview",
   download: "Download",
   downloading: "Downloading…",