Revoke Import Token

Revoke this user's share-extension token(s). The app calls this on sign-out: the token is independent of the Stytch session, so logout must kill it explicitly or the extension could keep importing for the user who just left (the shared-Keychain copy is wiped client-side in parallel).

Guests can revoke too, mirroring mint: a guest's token is scoped to that guest's user_id, so the same one-token-per-user cleanup applies.