🔨(backend) make the 'language' attribute on the User model nullable

- allow the language on the user to be unset
- set the default language to be unset
- helps us determine that the user has yet to set a language preference

src/backend/core/migrations/0019_alter_user_language_default_to_null.py

@@ -0,0 +1,36 @@
+# Generated by Django 5.1.5 on 2025-03-04 12:23
+from django.db import migrations, models
+
+import core.models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("core", "0018_update_blank_title"),
+    ]
+
+    operations = [
+        migrations.AlterModelManagers(
+            name="user",
+            managers=[
+                ("objects", core.models.UserManager()),
+            ],
+        ),
+        migrations.AlterField(
+            model_name="user",
+            name="language",
+            field=models.CharField(
+                blank=True,
+                choices=[
+                    ("en-us", "English"),
+                    ("fr-fr", "Français"),
+                    ("de-de", "Deutsch"),
+                ],
+                default=None,
+                help_text="The language in which the user wants to see the interface.",
+                max_length=10,
+                null=True,
+                verbose_name="language",
+            ),
+        ),
+    ]