feat: Completely rework notification framework

This change is needed as
a) there are many different types of notifications. A notification about a new comment does not only relate the comment but also adoption notice and a user that made the comment. Therefore, I introduce a new general notification that has optional links to other objects.
b) this change allows to define a different representation of e-mails vs. display on the website. The new notification type is in charge of representation from now on. Title and text will be deprecated and eventually removed

src/fellchensammlung/migrations/0052_remove_basenotification_user_and_more.py

@@ -0,0 +1,54 @@
+# Generated by Django 5.2.1 on 2025-07-11 09:01
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fellchensammlung', '0051_rescueorganization_parent_org_speciesspecialization'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='basenotification',
+            name='user',
+        ),
+        migrations.RemoveField(
+            model_name='commentnotification',
+            name='basenotification_ptr',
+        ),
+        migrations.RemoveField(
+            model_name='commentnotification',
+            name='comment',
+        ),
+        migrations.CreateModel(
+            name='Notification',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('read_at', models.DateTimeField(blank=True, null=True, verbose_name='Gelesen am')),
+                ('notification_type', models.CharField(choices=[('new_user', 'Useraccount wurde erstellt'), ('new_report_an', 'Vermittlung wurde gemeldet'), ('new_report_comment', 'Kommentar wurde gemeldet'), ('an_is_to_be_checked', 'Vermittlung muss überprüft werden'), ('an_was_deactivated', 'Vermittlung wurde deaktiviert'), ('an_for_search_found', 'Vermittlung für Suche gefunden')], max_length=200, verbose_name='Benachrichtigungsgrund')),
+                ('title', models.CharField(max_length=100, verbose_name='Titel')),
+                ('text', models.TextField(verbose_name='Inhalt')),
+                ('read', models.BooleanField(default=False)),
+                ('adoption_notice', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='fellchensammlung.adoptionnotice', verbose_name='Vermittlung')),
+                ('comment', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='fellchensammlung.comment', verbose_name='Antwort')),
+                ('report', models.ForeignKey(help_text='Report auf den sich die Benachrichtigung bezieht.', on_delete=django.db.models.deletion.CASCADE, to='fellchensammlung.report', verbose_name='Report')),
+                ('user_related', models.ForeignKey(help_text='Useraccount auf den sich die Benachrichtigung bezieht.', on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL, verbose_name='Verwandter Useraccount')),
+                ('user_to_notify', models.ForeignKey(help_text='Useraccount der Benachrichtigt wird', on_delete=django.db.models.deletion.CASCADE, related_name='user', to=settings.AUTH_USER_MODEL, verbose_name='Nutzer*in')),
+            ],
+        ),
+        migrations.DeleteModel(
+            name='AdoptionNoticeNotification',
+        ),
+        migrations.DeleteModel(
+            name='BaseNotification',
+        ),
+        migrations.DeleteModel(
+            name='CommentNotification',
+        ),
+    ]

src/fellchensammlung/migrations/0053_alter_notification_adoption_notice_and_more.py

@@ -0,0 +1,40 @@
+# Generated by Django 5.2.1 on 2025-07-11 09:10
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fellchensammlung', '0052_remove_basenotification_user_and_more'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='notification',
+            name='adoption_notice',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='fellchensammlung.adoptionnotice', verbose_name='Vermittlung'),
+        ),
+        migrations.AlterField(
+            model_name='notification',
+            name='notification_type',
+            field=models.CharField(choices=[('new_user', 'Useraccount wurde erstellt'), ('new_report_an', 'Vermittlung wurde gemeldet'), ('new_report_comment', 'Kommentar wurde gemeldet'), ('an_is_to_be_checked', 'Vermittlung muss überprüft werden'), ('an_was_deactivated', 'Vermittlung wurde deaktiviert'), ('an_for_search_found', 'Vermittlung für Suche gefunden'), ('new_comment', 'Neuer Kommentar')], max_length=200, verbose_name='Benachrichtigungsgrund'),
+        ),
+        migrations.AlterField(
+            model_name='notification',
+            name='report',
+            field=models.ForeignKey(blank=True, help_text='Report auf den sich die Benachrichtigung bezieht.', null=True, on_delete=django.db.models.deletion.CASCADE, to='fellchensammlung.report', verbose_name='Report'),
+        ),
+        migrations.AlterField(
+            model_name='notification',
+            name='user_related',
+            field=models.ForeignKey(blank=True, help_text='Useraccount auf den sich die Benachrichtigung bezieht.', null=True, on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL, verbose_name='Verwandter Useraccount'),
+        ),
+        migrations.AlterField(
+            model_name='notification',
+            name='user_to_notify',
+            field=models.ForeignKey(blank=True, help_text='Useraccount der Benachrichtigt wird', null=True, on_delete=django.db.models.deletion.CASCADE, related_name='user', to=settings.AUTH_USER_MODEL, verbose_name='Nutzer*in'),
+        ),
+    ]