Support %guest_portal% shortcode in Canned Responses

Problem: The %guest_portal% shortcode is currently supported in automated messaging rules but not in canned responses.

Current Workaround: Hosts must manually copy the Guest Portal link from the reservation sidebar in the Inbox and paste it into the message.

Impact: This adds manual effort and defeats the efficiency of using saved responses, especially when sending deposit instructions.

Proposed Solution: Enable the %guest_portal% shortcode to function within canned responses, allowing the reservation-specific link to populate automatically.

Unlock: Hosts will be able to send personalized guest portal links instantly via canned responses, saving time and reducing manual errors.