feat(skills): add Java Spring Boot skills
Adds 6 new skills for Java Spring Boot development:
- java-coding-standards: naming, immutability, Optional, streams
- springboot-patterns: REST API, service layer, caching, async
- springboot-tdd: JUnit 5, Mockito, MockMvc, Testcontainers
- springboot-security: Spring Security, validation, CSRF
- springboot-verification: Maven/Gradle build verification
- jpa-patterns: entity design, relationships
Thanks @examin!
manish sharma