♻️(backend) increase user short_name field length

The user's short_name field length was set to 20. This is not enought
and we have some users who cannot register because of that. We changed
this length to a higher one, 100, like the full_name.

src/backend/core/migrations/0025_alter_user_short_name.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.2.7 on 2025-10-22 06:12
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("core", "0024_add_is_masked_field_to_link_trace"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="user",
+            name="short_name",
+            field=models.CharField(
+                blank=True, max_length=100, null=True, verbose_name="short name"
+            ),
+        ),
+    ]

src/backend/core/models.py

@@ -148,7 +148,9 @@ class User(AbstractBaseUser, BaseModel, auth_models.PermissionsMixin):
     )
 
     full_name = models.CharField(_("full name"), max_length=100, null=True, blank=True)
-    short_name = models.CharField(_("short name"), max_length=20, null=True, blank=True)
+    short_name = models.CharField(
+        _("short name"), max_length=100, null=True, blank=True
+    )
 
     email = models.EmailField(_("identity email address"), blank=True, null=True)