feat(docs): 文档站重制 — 参照 opsxapi/opsxshell 体系,服务端渲染三栏布局

- 后端 goldmark 渲染管线:/docs/:slug 页面 + /docs/search-data.json 搜索索引,
  manifest.json 驱动分组导航,正文剥 H1 避免与页面头重复
- 三栏布局(分组侧栏/内容/本页目录)+ 顶栏(品牌/版本徽章/搜索面板/官网入口),
  docs.css 品牌绿版 + docs.js(代码复制/轻量高亮/提示块/TOC 滚动高亮/移动端抽屉)
- 替换 docsify;无上一页时空占位无边框;visual-judge 两轮评审(初版 fail → 修复后 pass)

backend/go.sum

@@ -170,6 +170,8 @@ github.com/x448/float16 v0.8.4 h1:qLwI1I70+NjRFUR3zs1JPUCgaCXSh3SW62uAKT1mSBM=
 github.com/x448/float16 v0.8.4/go.mod h1:14CWIYCyZA/cWjXOioeEpHeN/83MdbZDRQHoFcYsOfg=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
+github.com/yuin/goldmark v1.8.6 h1:d0VcaP1sx9GkFVkoW+KtggpGi2KZ965i14b0+bDQST4=
+github.com/yuin/goldmark v1.8.6/go.mod h1:ip/1k0VRfGynBgxOz0yCqHrbZXhcjxyuS66Brc7iBKg=
 go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
 go.yaml.in/yaml/v2 v2.4.2/go.mod h1:081UH+NErpNdqlCXm3TtEran0rJZGxAYx9hb/ELlsPU=
 go.yaml.in/yaml/v3 v3.0.3 h1:bXOww4E/J3f66rav3pX3m8w6jDE4knZjGOw8b5Y6iNE=