Add database initialization script

- Add database/init.sql with schema
- Mount init.sql in docker-compose for auto-initialization
- PostgreSQL will run this on first startup

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -11,6 +11,7 @@ services:
       POSTGRES_DB: priceghost
     volumes:
       - postgres_data:/var/lib/postgresql/data
+      - ./database/init.sql:/docker-entrypoint-initdb.d/init.sql:ro
     ports:
       - "5432:5432"
     healthcheck: