Add compose services for local stack

[BojayL]

Summary

• Add gateway and API services to docker-compose alongside Postgres.
• Expose gateway on port 8080 and API on port 8081 with container health checks.
• Fix the initial SQL migration comment syntax so startup migrations run under Postgres.
• Document the compose development flow and health check endpoints.

Fixes #1

Validation

• docker compose config
• docker compose build waveflow-gateway waveflow-api
• docker compose up -d
• curl -fsS http://localhost:8080/health
• curl -fsS http://localhost:8081/health
• git diff --check