Status-aware WhatsApp prefill message

The WhatsApp click-to-chat button renders for both pending and confirmed reservations, but the prefilled message was written for pending only. Tapping it on a confirmed booking sent the customer a vague enquiry; worse, a fixed "confirmed" wording would have told customers with a still-pending booking that their table was secured.

The message now branches on the same $is_confirmed check that already drives the status pill and the admin CTA, so the three can never disagree. Confirmed bookings get an explicit confirmation; pending wording is unchanged.

Escaping and digit validation untouched.