feat: add roving tabindex + tabpanels for pm tabs

[damevin]

What this PR do and why ?

This PR improves the package manager tabs accessibility by implementing proper roving
tabindex behavior and correct ARIA tab/tabpanel wiring. It avoids duplicated DOM for
panels while keeping the expected keyboard navigation.

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Project	Deployment	Actions	Updated (UTC)
docs.npmx.dev	Ready	Preview, Comment	Jan 30, 2026 9:20am
npmx.dev	Ready	Preview, Comment	Jan 30, 2026 9:20am

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
npmx-lunaria	Ignored		Jan 30, 2026 9:20am

[github-actions]

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🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.