Get Onboarding Route

Return the next onboarding step. If this doesn't answer your question, call start_inquiry to ask 4chems directly or request a call.

Anonymous call (no token): returns action=register with no URL and a next_step naming start_account_registration and start_device_login (UC-091). A presented but invalid/expired token returns 401 (no silent fallback).

Authenticated call: existing routing logic (email_verified gate, domain lookup, etc.) — behaviour is unchanged from pre-UC-053 (UC-014). The email domain is derived from the token's email claim only. Zero DB reads are performed before the email_verified gate (NFR-006 pt 3).