Extract pure JSON DTOs into internal/serviceapi so web no longer imports
server. Add $HC wire type, persist assigned beacons, fix ValidATC before
first position, and prevent double leave notifications.
Expose OnlineUserPilot.Synthetic on service HTTP /online_users so
operators and the dashboard can badge in-process sweatbox aircraft.
Enforce ≥95% hard coverage on internal/sweatbox in check-coverage.sh.
Introduce pure internal/sweatbox package with TWRTrainer-compatible
airport and scenario parsers, fixtures, unit tests, and import-graph
ownership rules. No server wiring.