feat: add description and shortcuts to header menu registration

[roncodes]

Summary

Adds a description and shortcuts array to the registerHeaderMenuItem call in addon/extension.js, following the pattern established in the Ledger engine.

Each shortcut entry provides:

• title — human-readable section name
• description — one-line summary of what the section does
• icon — FontAwesome icon name
• route — the Ember route to transition to on click

Shortcuts added: Users, Drivers, Customers, Groups, Roles, Policies

Changes

• addon/extension.js — expanded the options object passed to registerHeaderMenuItem with description and shortcuts

Testing

No logic changes. The shortcuts are purely declarative data consumed by the header menu component in @fleetbase/ember-ui.