Mobile API Contract
Give this surface to the app developer for first integration.
POST
/v1/users/meCreate/update signed-in user profilePOST
/v1/circlesCreate family circlePOST
/v1/circles/joinJoin by invite codePOST
/v1/locations/meSend latest GPS pointGET
/v1/locations/circles/{circleId}/latestMap view for membersPOST
/v1/sosCreate emergency alertSocket.io
/realtime
Use Firebase ID token in auth.token, then emit circle:join and location:update.