Library theming: Update Masthead component in design kit

[patternfly-jira-sync]

Update the Masthead component in the PatternFly design kit to align with the unified theme. Update Figma files, styles, documentation, and ensure unified visual consistency throughout.

Deliverables:

• Update tokens

• Include new variants

• Update branded icons

• Address audit fixes:

• Boolean inconsistency updates (checklist here)

• Add some extra utility item slots within the masthead

• Horizontal nav resize & alignment issues:

  • Fix alignment (should be centered on masthead)

  • Fix placement? Should it be that far from the PF logo?

  • Fix auto layout (doesn't move when resizing)

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Jira Issue: PF-3920