**Related issue:** Resolves#42879
* Full UI for API-only user management: create/edit flows, fleet/role
assignment, selectable API endpoint permissions, and one-time API key
display.
* New reusable components: API user form, endpoint selector, API access
section, and API key presentation.
* Admin workflow switched from in-page modals to dedicated pages and
streamlined action dropdown navigation.
* Layout and styling refinements for user management, team lists, and
dropdown behaviors.
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Co-authored-by: Juan Fernandez <juan@fleetdm.com>
