Use a selector to choose a problem number

apps/participation/models.py

@@ -4,12 +4,14 @@
 import os
 
 from address.models import AddressField
+from django.conf import settings
 from django.core.validators import RegexValidator
 from django.db import models
 from django.db.models import Index
 from django.urls import reverse_lazy
 from django.utils import timezone
 from django.utils.crypto import get_random_string
+from django.utils.text import format_lazy
 from django.utils.translation import gettext_lazy as _
 from registration.models import VolunteerRegistration
 from tfjm.lists import get_sympa_client
@@ -331,6 +333,9 @@ class Solution(models.Model):
 
     problem = models.PositiveSmallIntegerField(
         verbose_name=_("problem"),
+        choices=[
+            (i, format_lazy(_("Problem #{problem}"), problem=i)) for i in range(1, settings.PROBLEM_COUNT + 1)
+        ],
     )
 
     final_solution = models.BooleanField(