add SevenContext component to allow theming via tailwind-variants

[ionlizarazu]

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.
Read details.

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• I signed and returned the Plone Contributor Agreement, and received and accepted an invitation to join a team in the Plone GitHub organization.
• I verified there aren't other open pull requests for the same change.
• I followed the guidelines in Contributing to Volto.
• 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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[github-actions]

Hi There! 👋

We haven't seen any activity on this pull request in a while 😴, and we want to make sure that it's still relevant. Please let us know by:

• adding a comment about what needs to be done next 💬
• updating its status and other labels 🏷️

Otherwise close this pull request. 🧹

[sneridagh]

Important

Hello! Thanks for contributing to Plone Aurora! FYI, since June 5th, Plone Aurora lives in its own repository, thus, the seven branch does not accept any merges. If you want to merge your PR, please follow instructions: #8318
Sorry for the inconvenience!