Link online bookings to patients from calendar

About this issue

When an online booking does not match an existing patient, staff can currently link it to a patient from the pre-consult screen. Add the same capability directly to the calendar appointment details, so staff do not have to enter pre-consult just to link the booking. Acceptance criteria: - For an unmatched online booking, show a clear Link to existing patient action in the calendar appointment details. - Staff can search for and select an existing patient, review the selection, and confirm the link using the same matching/linking behaviour as pre-consult. - After linking, the calendar and pre-consult show the same linked patient and retain the booking's appointment details and notes. - Cancel makes no changes. Failed saves show an error and do not appear successful. Prevent duplicate linking or accidentally replacing a link that changed while the action was open. - Preserve existing practice access boundaries and staff permissions. Keep the current pre-consult linking workflow working. - Cover successful linking, cancel, no matching search results, failed save, and an appointment already linked by another staff member. Requested by Calvin on 5 November 2026, with screenshots of the consultations view and calendar appointment details. Screenshots are not attached; no patient names or contact details are copied into this task. Tracking only: keep New. Do not start implementation or deployment.