fix: return patient national code from profile in patients list

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>

docs/api/patient.md

@@ -45,9 +45,13 @@ Returns a paginated list of patient records belonging to the authenticated entit
       "uuid": "...",
       "entity_type": "doctor",
       "entity_id": 5,
-      "user": { "uuid": "...", "fullName": "علی رضایی", "phone": "09123456789" },
+      "user_uuid": "...",
+      "user_name": "علی رضایی",
+      "user_mobile": "09123456789",
+      "user_national_code": "0012345675",
+      "record_number": "1024",
+      "tags": [],
       "created_by_type": "doctor",
-      "created_by_id": 5,
       "created_at": 1718375000
     }
   ],
@@ -59,6 +63,8 @@ Returns a paginated list of patient records belonging to the authenticated entit
 }
 ```
 
+> `user_national_code` منبعِ حقیقتش جدول `profiles` است (نه `users`). اگر روی خودِ کاربر خالی باشد، از پروفایل پر می‌شود؛ اگر هیچ‌کدام نداشته باشند `null` است.
+
 **Errors:**
 
 | Code | HTTP | Description |