feat(core): app menu polish for NC34

[pringelmann]

Summary

Two follow-ups to #60180:

• Grid padding moves to the popover wrapper so the top-row hover sits inside the rounded corner.
• Admin pages (Settings, Apps, Accounts, Help) showed an empty current-app slot. Those entries register as type=settings so they're excluded from the apps initial state. Falls back to settingsNavEntries when no app is active. Logout filtered out defensively.

Aria-label includes the section name so screen readers match the visible text, and settings icons are force-whitened since they ship dark and would otherwise be invisible on the themed header.

Three unit tests cover the fallback path.

Also attempted to unify the two triggers visually. Three approaches, none clean enough before freeze. Parking for a post-NC34 design pass.

Checklist

• Code is properly formatted
• Sign-off on all commits
• Unit tests included
• Screenshots before/after below
• Documentation has been updated or is not required
• Backports requested where applicable
• Labels added where applicable
• Milestone added for target branch