Add Java-to-Kotlin conversion skill

[e5l]

Summary

• Adds kotlin-tooling-java-to-kotlin skill for converting Java source files to idiomatic Kotlin
• Extracts the conversion methodology from the j2k-vscode extension: 4-step precognition process (faithful translation → nullability → collections → idioms) with 5 invariants checked at each step
• Includes framework-aware conversion guidance for 12 frameworks, each in a separate reference file loaded only when matching imports are detected:
  • Spring — constructor injection, @Value escaping, @Bean/@Transactional openness
  • Lombok — full annotation removal and Kotlin equivalent mapping
  • Hibernate/JPA — open entities, no data classes, annotation site targets
  • Jackson — @field:/@get: dual annotation site targets
  • Micronaut — constructor injection, AOP openness
  • Quarkus — CDI no-arg constructors, Panache entities
  • Dagger/Hilt — @Inject constructor syntax, object modules
  • RxJava — Observable/Single/Completable → Flow/suspend mapping
  • JUnit/TestNG — JUnit 4→5 migration, kotlin.test assertions
  • Guice — module binding DSL, @Named site targets
  • Retrofit/OkHttp — Call<T> → suspend, interceptor SAM conversion
  • Mockito — MockK conversion table and mockito-kotlin alternative
• Includes known issues reference (keyword conflicts, SAM ambiguity, platform types, etc.)
• Includes post-conversion verification checklist

Test plan

• CI validates skill directory naming convention (kotlin-tooling-java-to-kotlin)
• CI validates SKILL.md frontmatter via Flash-Brew-Digital/validate-skill action
• Manual test: convert a sample Java file using the skill's methodology
• Verify framework detection table covers all 12 reference files

🤖 Generated with Claude Code

[e5l]

@evilya could you please check why the CI status is stuck?

[evilya]

@e5l I guess #19 should fix it, but it might require us to re-trigger workflows. You can ignore it for now

[e5l]

The merge is blocked for me cause I'm not the owner. If you need help with reviewing feel free to add me in

[evilya]

Same, I also don't have permission to merge without checks. @Tapchicoma said he would take a look at it

[d-ambatenne]

@e5l have also evaled this one as the skills in the backend repo?

[e5l]

Yep, it's the essence of the agent we built for the j2k during internship