feat: improve Docker deployment and Dify API configuration

- Use environment variables for Dify API key/URL
- Add host.docker.internal support in docker-compose
- Add DATABASE_URL env and prisma db push to Dockerfile
- Clean up test/requirement files and add deployment docs

docker-compose.yml

@@ -4,10 +4,14 @@ services:
     build: .
     ports:
       - "3000:3000"
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     environment:
       - DATABASE_URL=file:/app/data/dev.db
       - NEXTAUTH_SECRET=nextapp-secret-key-2026
       - NEXTAUTH_URL=http://localhost:3000
+      - DIFY_API_URL=http://host.docker.internal/v1/chat-messages
+      - DIFY_API_KEY=app-lbe2lglt7taGtZk0dG7pAhbx
     volumes:
-      - /opt/nextapp/data/dev.db:/app/data/dev.db
+      - ./prisma/dev.db:/app/data/dev.db
     restart: unless-stopped