feat(docs): 用户手册接入界面截图

- 6 张核心页面截图(仪表盘/向导/日志查询/日志分析/告警/设置)存 docs/assets/screenshots,
  随发布包分发;产品介绍页新增「界面预览」两列网格,各功能页顶部内嵌对应截图
- goldmark 开启 WithUnsafe 以渲染网格 HTML(文档自维护,无注入面);截图经 DOM 校验全部加载成功

backend/services/docsite.go

@@ -15,6 +15,7 @@ import (
 	"github.com/yuin/goldmark"
 	"github.com/yuin/goldmark/extension"
 	"github.com/yuin/goldmark/parser"
+	htmlRenderer "github.com/yuin/goldmark/renderer/html"
 )
 
 // DocsManifest docs/user-guide/manifest.json
@@ -57,7 +58,7 @@ type DocsNav struct {
 var (
 	docsManifestCache *DocsManifest
 	docsBasePath      string
-	docsMD            = goldmark.New(goldmark.WithExtensions(extension.Table), goldmark.WithParserOptions(parser.WithAutoHeadingID()))
+	docsMD            = goldmark.New(goldmark.WithExtensions(extension.Table), goldmark.WithParserOptions(parser.WithAutoHeadingID()), goldmark.WithRendererOptions(htmlRenderer.WithUnsafe()))
 	docsTOCPattern    = regexp.MustCompile(`<h([23]) id="([^"]+)"[^>]*>([^<]+)</h[23]>`)
 )