Fix header tools so login and logout are not both shown after authent…

[aryan7081]

Fixes #161

This issue happened because the development header tools in packages/layout/slots/Tools.tsx always rendered both /login and /logout and never read authentication state. The root loader already exposes isAuthenticated, but the tools slot ignored it, so both links stayed visible after a successful login.

This fix reads isAuthenticated from the root loader and shows only Log in for anonymous visitors and only Log out for authenticated users. It keeps the links development-only, uses translated labels with English fallbacks, and adds a layout news fragment for the changelog.

Caution

The Volto Team has suspended its review of new pull requests from first-time contributors until the release of Plone 7, which is preliminarily scheduled for the second quarter of 2026.
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• I verified there aren't other open pull requests for the same change.
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• I succesfully ran code linting checks on my changes locally.
• I succesfully ran unit tests on my changes locally.
• I succesfully ran acceptance tests on my changes locally.
• If needed, I added new tests for my changes.
• If needed, I added documentation for my changes, either in the Storybook or narrative documentation.
• I included a change log entry in my commits.

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