Per-user controls for concurrent sessions and aircraft view scope

Problem:

Today there are no per-user controls for limiting how many simultaneous sessions a user can have, and visibility into aircraft data is largely all-or-nothing — admins can't restrict a user or group to only the current position of active aircraft (vs. last track or full history).

Desired outcome:

Admins can configure, per user or group, both how many concurrent sessions are allowed (e.g. 1 web + 1 mobile) and what level of aircraft data the user is permitted to see.

Proposed change:

Add per-user (and ideally per-group) settings for: (1) maximum concurrent sessions per platform, with a clear error when an additional login is attempted; (2) aircraft view scope — current positions only, last track, or full history.