Session-swap is now the only flow. Legacy /fp/tablet/unlock endpoint
deleted. _tablet_audit.py (env_for_tablet_tech helper) deleted with
its last caller gone. /fp/tablet/ping no longer takes current_tech_id
(session uid IS the tech). /fp/tablet/tiles drops tablet_session_mode
return key (kiosk_uid + current_uid retained for OWL isLocked logic).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>