Stage 13: MongoDB connectivity
Use JDK 21+ and Maven 3.9+.
Open README.html for Atlas setup and complete instructions.
Set MONGODB_URI and MONGODB_DATABASE=spring_stage13_products in your terminal.
Run mvn spring-boot:run in the folder containing pom.xml.
Open http://localhost:8091/database-info then /products.
Stop with Ctrl+C.
