Stage 14: Todo list application
Same todo-mvc source as the later Spring Boot MVC manual.
Read README.html for setup, concept mapping and complete source.
JDK 21+ and Maven 3.9+. Set MONGODB_URI in the launching terminal.
Run mvn spring-boot:run in the folder containing pom.xml.
Open http://localhost:8080/todos (change server.port if busy).
Database: todo_mvc; collection: todos. Stop with Ctrl+C.
