Remove focus outline for links and buttons in navigation

[aaronmgn]

Description

Navbar links and buttons no longer keep a focus ring stuck on them after a mouse click. The rule removes the outline only for pointer focus :focus:not(:focus-visible), so the focus ring still appears for keyboard navigation.

Switching the behavior to :focus-visible removes the lingering ring for mouse users while preserving it for keyboard users too.

Motivation and Context

An easy fix that was easy to resolve.

#26503

How Has This Been Tested?

Manually, on a local dev stack (Graylog 7.2.0-SNAPSHOT, Chromium):

• Built and deployed the change: confirmed the running server serves the rebuilt bundle.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have requested a documentation update.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[CLAassistant]

All committers have signed the CLA.