fix(sidebar): add groups for namespaced plugins

[ryzrr]

Summary

Add groups for namespaces ,whose generated pages had no catagory , so they were reachable through URL only

What kind of change does this PR introduce?
Fix

Did you add tests for your changes?
no

Does this PR introduce a breaking change?
no

If relevant, what needs to be documented once your changes are merged or what have you already documented?
no

Use of AI
for verifying only

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
webpack-doc-kit	Ready	Preview	Jul 31, 2026 6:23pm

[github-actions]

⚡ Lighthouse report

Audited the Vercel preview deployment: https://webpack-doc-6tdp9eqah-openjs.vercel.app

URL	Performance	Accessibility	Best Practices	SEO	Report
/	🟢 95	🟢 96	🟢 96	🟢 100	🔗
/about	🟢 99	🟢 97	🟢 100	🟢 100	🔗
/about/sponsors	🟠 85	🟢 95	🟢 100	🟢 100	🔗
/blog	🟢 99	🟢 96	🟢 100	🟢 100	🔗
/blog/posts/2026-02-04-roadmap-2026	🟢 98	🟢 93	🟢 100	🟢 100	🔗
/guides/getting-started	🟢 93	🟢 97	🟢 100	🟢 100	🔗
/docs/api/options	🔴 68	🟢 96	🟢 100	🟢 100	n/a
/docs/loaders/css-loader	🟢 99	🟢 97	🟢 100	🟠 83	🔗

Scores are advisory (warn at 90); they do not fail the build. See .lighthouserc.json.

[ryzrr]

Also these 5 parity pages bring siblings with it !

[bjohansebas]

hmm, twice overviews

[ryzrr]

Looks like the experiment nest two child namespaces. we can add this in the site.mjs ?

 if (url.endsWith('/index.md')) {
    return getPathDepth(url) === 2 ? 'Overview' : target.name;
  }