fix: prevent blocksClipboard persistence for anonymous users

[pratyush07-hub]

This PR fixes an issue where Volto was creating localStorage entries even for anonymous users.
The problem comes from the blocksClipboard reducer being configured as persistent. Even though anonymous users can’t copy or paste blocks, Volto would still create an empty localStorage entry, which isn’t really needed and can be a concern from a privacy (GDPR) point of view.
With this change, Redux state is only saved to localStorage after a user is logged in. For anonymous visitors, nothing is stored.

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This PR fixes the issue by:

1. Check if the user is logged in
   We only act when the user has a valid session (userSession.token).
2. Save data only for logged-in users
   The clipboard and other persistent data are stored in the browser only when someone is logged in; anonymous visitors are skipped.
3. Keep browsers clean and private
   Anonymous users no longer get empty localStorage entries, improving privacy and GDPR compliance, while editors’ behavior stays the same.

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If your pull request closes an open issue, include the exact text below, immediately followed by the issue number. When your pull request gets merged, then that issue will close automatically.

Closes #6997

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[pratyush07-hub]

@wesleybl The issue is closed as completed, and this PR implements the suggested fix.
I’m happy to update the implementation if you’d prefer a different approach.