XWiki Unified top bar work

Following last mockups from May 2025, more information available on the project's internal repository.

This task will scope:

• Allocate implementation role between product and client team (to define what will be improved in XWiki standard and delivered as customization for openDesk image)
• Improve XWiki top left logo to easily redirect to openDesk portal
• Edit UI to fit OD design
• Test
• Release

For reference, here is our current status:

• https://forum.xwiki.org/t/duplication-of-user-profile-on-xwiki-header/14041
• https://design.xwiki.org/xwiki/bin/view/Proposal/Userprofileaccessandsidebarrevamps