Add n8n community node, /api/v1/render alias, and job webhooks for OSS automation.

Payment-free self-hosted builds keep full API access with optional webhookUrl callbacks and the published n8n-nodes-songs2vid package source under integrations/n8n.

prisma/schema.prisma

@@ -59,6 +59,8 @@ model Job {
   user        User      @relation(fields: [userId], references: [id], onDelete: Cascade)
   status      JobStatus @default(PENDING)
   imagePath   String
+  /// Optional absolute http(s) URL for n8n / automation callbacks
+  webhookUrl  String?
   items       JobItem[]
   createdAt   DateTime  @default(now())
   completedAt DateTime?