feat(footer): group social links under the brand column and add Bluesky

[ryzrr]

Summary
Repositions the social handle of webpack inside the footer

What kind of change does this PR introduce?
feat

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
no

[vercel]

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

Project	Deployment	Actions	Updated (UTC)
webpack-doc-kit	Ready	Preview	Aug 8, 2026 8:07pm

[github-actions]

⚡ Lighthouse report

Audited the Vercel preview deployment: https://webpack-doc-jcvd3uezz-openjs.vercel.app

URL	Performance	Accessibility	Best Practices	SEO	Report
/	🟢 95	🟢 96	🟢 100	🟢 100	🔗
/about	🟢 99	🟢 97	🟢 100	🟢 100	🔗
/about/sponsors	🟠 84	🟢 95	🟢 96	🟢 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.