National code is stored on the profiles table, not users, so the patients
search returned null user_national_code for patients that actually have one
— which blocked selecting an existing patient on the appointment create
form. Backfill user_national_code from the profile (batch query) in the
list endpoint. On the create page, show a picked patient's stored national
code read-only and only prompt for input when the record genuinely lacks
one. Add backend tests and update docs/api/patient.md.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
