fix: configure CI database connection properly

- Add dotenv loading to Django settings
- Update CI workflow to use correct environment variables
- Set POSTGRES_* variables instead of DATABASE_URL
- Add environment variables to all Django management commands
- Fixes CI test failures due to database connection issues

app/stiftung/migrations/0025_appconfiguration.py

@@ -0,0 +1,37 @@
+# Generated by Django 5.0.6 on 2025-08-31 22:08
+
+import uuid
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stiftung', '0024_dokumentlink_abrechnung_id'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='AppConfiguration',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ('key', models.CharField(max_length=100, unique=True, verbose_name='Setting Key')),
+                ('display_name', models.CharField(max_length=200, verbose_name='Display Name')),
+                ('description', models.TextField(blank=True, null=True, verbose_name='Description')),
+                ('value', models.TextField(verbose_name='Value')),
+                ('default_value', models.TextField(verbose_name='Default Value')),
+                ('setting_type', models.CharField(choices=[('text', 'Text'), ('number', 'Number'), ('boolean', 'Boolean'), ('url', 'URL'), ('tag', 'Tag Name'), ('tag_id', 'Tag ID')], default='text', max_length=20, verbose_name='Type')),
+                ('category', models.CharField(choices=[('paperless', 'Paperless Integration'), ('general', 'General Settings'), ('notifications', 'Notifications'), ('system', 'System Settings')], default='general', max_length=50, verbose_name='Category')),
+                ('is_active', models.BooleanField(default=True, verbose_name='Active')),
+                ('is_system', models.BooleanField(default=False, verbose_name='System Setting (read-only)')),
+                ('order', models.IntegerField(default=0, verbose_name='Display Order')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+            ],
+            options={
+                'verbose_name': 'App Configuration',
+                'verbose_name_plural': 'App Configurations',
+                'ordering': ['category', 'order', 'display_name'],
+            },
+        ),
+    ]