Let hosts re-ask a guest for their phone number after check-in form is submitted

If a guest completed the Guest Portal check-in form but entered the wrong phone number (typo, landline, etc.), there's no way for the host to prompt them to correct it.

• Host-triggered action on a reservation: "Ask guest to re-enter phone number," which sends the guest a fresh Guest Portal link with a small task asking them to confirm / update their number, along with an optional host-authored explanation ("we need a different number for SMS updates").
• Should overwrite the reservation's phone field once submitted.

Would also help hosts who realise post-check-in that they need an SMS-capable number for the guest.