request-access / demo / register / verify / verify-resend / password-login /
password-reset(request|confirm) / set-password each took an untyped `payload:
dict` and hand-picked fields with `.get(...)`. Replace with five small BaseModels
(EmailIn, EmailPasswordIn, TokenIn, TokenPasswordIn, SetPasswordIn) so FastAPI
validates the body shape and publishes the schema. Fields are `str | None` to
preserve exact behaviour — a missing/null field still coerces via the existing
`(... or "")`, no stricter 422s. Green under the auth-session suite (7), ruff clean.