feat: add Attachment model and implement file permission checks for media access

backend/server/adventures/migrations/0018_attachment.py

@@ -0,0 +1,26 @@
+# Generated by Django 5.0.8 on 2025-01-19 00:39
+
+import django.db.models.deletion
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('adventures', '0017_adventureimage_is_primary'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Attachment',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False, unique=True)),
+                ('file', models.FileField(upload_to='attachments/')),
+                ('adventure', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='attachments', to='adventures.adventure')),
+                ('user_id', models.ForeignKey(default=1, on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL)),
+            ],
+        ),
+    ]