fix: add detached exec launch metadata

[acmore]

Summary

• write per-job detached exec metadata under /tmp/okdev-exec in the target container
• print job id, pid, log path, and metadata path when detach launch succeeds
• treat missing or malformed detach launch metadata as a launch failure

Test Plan

• go test ./internal/cli
• .venv/bin/pre-commit run --all-files --hook-stage manual okdev-gofmt