[Chore] Create project skills and fix STDOUT logging

[Wikijito7]

Created 7 reusable skills under .agents/skills/ and replaced all println() calls with proper SLF4J logging.

Skills created

• testing-ktor — Ktor test patterns with MockK, coroutines test, JaCoCo
• ci-cd-sonar — CI workflows, SonarCloud, version catalog, fatJAR
• error-handling — AcknowledgeBO vs exceptions, response codes, logging
• config-management — HOCON loading, app.conf, multi-source config
• background-tasks — Coroutine-based periodic tasks, error handling
• serialization-validation — @SerialName conventions, validation patterns
• monitoring-logging — Micrometer/Prometheus, SLF4J, CallLogging

Logging fixes

Replaced 6 println() calls with logger.error() in:

• EmailService.kt
• RecoverLocalDataSource.kt
• VerifyLocalDataSource.kt
• UserLocalDataSource.kt