feat: [SKILL-27] Kotlin runtime foundation and persistence core

[Sermilion]

Summary

Build the JVM-only runtime-kotlin/ foundation for SKILL-27 and carry it into Phase 2 persistence core, while keeping the existing Python runtime as the source of truth.

• scaffold the initial Kotlin runtime module, package boundaries, contract/error primitives, smoke tests, and starter-aligned Gradle build logic under runtime-kotlin/
• add a raw SQLite/JDBC persistence foundation in runtime-kotlin with DB path resolution, schema bootstrap, additive migrations/backfills, telemetry outbox storage, and feature workflow row persistence
• document the SQLite/JDBC dependency decision and Phase 2 carryover state in the migration note and saved feature spec

Feature Flags

N/A

How Has This Been Tested?

1. .venv/bin/python3 -m unittest discover -s tests
2. .venv/bin/python3 -m skill_bill.cli version
3. (cd runtime-kotlin && ./gradlew check detekt spotlessCheck)
4. Expected result: the legacy Python runtime still passes its existing suite, and the new Kotlin runtime foundation plus persistence-core checks pass on the same branch.