Implements use cases across a Spring Boot + Spring Data JPA backend (flat single-module or hexagonal/ports-and-adapters multi-module) and an Angular frontend wired to that API. Use when the user asks to "implement a use case", "build the API", "create a REST endpoint", "write the data access layer", "build the Angular page/component", or mentions Spring Boot, JPA/Hibernate entities, hexagonal architecture, ports and adapters, or an Angular frontend calling a Java backend.