fix: relaunch updated runtime after self-update

[alexk-dev]

Summary

• add a runtime launcher that supervises the bot process and handles self-update restarts via exit code 42
• restart from the jar selected in current.txt instead of always booting the immutable image classpath after an update
• point the Jib container entrypoint at the launcher and cover bundled-runtime and staged-jar restart flows with tests

[sonarqubecloud]

Quality Gate failed

Failed conditions
66.1% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud