fix: K8s 健康检查 400 + 补充 generation 迁移文件

- 健康检查探针添加 Host: localhost 头，解决 Django ALLOWED_HOSTS 拒绝
- 补充 generation 0004 迁移（model choices 标签更新）

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/apps/generation/migrations/0004_alter_generationrecord_model.py

@@ -0,0 +1,18 @@
+# Generated by Django 4.2.29 on 2026-03-16 07:00
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('generation', '0003_generationrecord_ark_task_id_and_more'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='generationrecord',
+            name='model',
+            field=models.CharField(choices=[('seedance_2.0', 'AirDrama'), ('seedance_2.0_fast', 'AirDrama Fast')], max_length=30, verbose_name='模型'),
+        ),
+    ]

k8s/backend-deployment.yaml

@@ -93,6 +93,9 @@ spec:
           httpGet:
             path: /healthz/
             port: 8000
+            httpHeaders:
+            - name: Host
+              value: localhost
           initialDelaySeconds: 30
           periodSeconds: 10
           timeoutSeconds: 5
@@ -101,6 +104,9 @@ spec:
           httpGet:
             path: /healthz/
             port: 8000
+            httpHeaders:
+            - name: Host
+              value: localhost
           initialDelaySeconds: 15
           periodSeconds: 5
           timeoutSeconds: 3