feat: Attachment 모델 추가 및 관련 기능 구현

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

blog/migrations/0004_attachment.py

@@ -0,0 +1,25 @@
+# Generated by Django 4.2.14 on 2026-01-20 13:58
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('blog', '0003_tag_post_tags'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Attachment',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('file', models.FileField(upload_to='attachments/%Y/%m/%d/')),
+                ('original_name', models.CharField(max_length=255)),
+                ('file_size', models.PositiveIntegerField()),
+                ('uploaded_at', models.DateTimeField(auto_now_add=True)),
+                ('post', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='attachments', to='blog.post')),
+            ],
+        ),
+    ]