Validate the trial against the server.

#112 unit 3: behind the charging switch (get_charging_switch_date) this expresses a real 14-day trial counted from first connection, plus the 30-day grace an EXISTING machine is owed from the switch date S. The switch ships ABSENT, so pre-switch is BACKWARD-COMPATIBLE (#140 O2): the existing fields are unchanged (days_left 3650, never expired, same install_date) and it only ADDS state/code — not byte-identical, but no existing reader breaks. exempt_tools (the tools that keep working at expiry) is NOT echoed here: it is a client-enforced contract constant (GO answer b, in license-activation.v1.json).