Write docker-compose with pgvector + Kuzu volume

[krapfj23]

Summary

Create a docker-compose.yml that orchestrates the backend and PostgreSQL (pgvector) services with persistent volumes.

Note: The Kuzu volume may become unnecessary after the Neo4j Aura migration (#65-#67). For now, include it since Kuzu is the current graph store.

Blocked by

• Write Dockerfile + .dockerignore #53 (Dockerfile)

Blocks

• Document local dev setup with Docker #55 (Docker dev docs)
• Deploy to cloud + configure env vars #60 (deploy to cloud)

Steps

1. Create docker-compose.yml at repo root
2. Define backend service using the Dockerfile from Write Dockerfile + .dockerignore #53
3. Define db service using pgvector/pgvector:pg16 image with health check
4. Add a named volume for Kuzu storage (.cognee_system/databases/kuzu/)
5. Add a named volume for PostgreSQL data persistence
6. Configure environment variables via env_file: .env
7. Set depends_on: db with health check condition for the backend service

Acceptance Criteria

• docker-compose up starts both services
• Backend connects to pgvector DB successfully
• Data persists across docker-compose down / up cycles
• PR body includes Closes #54