Add docker-compose.yml, dev override, and .env.example

- docker-compose.yml: muse (app), postgres:16-alpine, qdrant services with healthcheck on postgres and named volumes for persistence - docker-compose.override.yml: dev mode — bind-mounts source dirs, enables uvicorn --reload, sets DEBUG=true - .env.example: template covering all required and optional env vars - Service named 'muse' to match existing seed/migration scripts