Agent Skills: springboot-migration

Migrate Spring Boot projects to version 4.0 with Java 25, including Spring Modulith 2.0 and Testcontainers 2.x upgrades. Use when user requests upgrading Spring Boot, migrating to Java 25, updating dependencies to Spring Boot 4, mentions Jackson 3 migration, asks about starter renames (web→webmvc, aop→aspectj), fixing test annotations (@MockBean→@MockitoBean), or needs help with Spring Modulith 2.0 or Testcontainers 2.x compatibility. Analyzes codebase for migration issues and guides through changes with specific file references.