Phase A4 of plans/implementation-plan-A-B.md. Implements the full job orchestrator (clone -> start -> wait -> probe -> build -> collect -> guaranteed cleanup) as a new commands/job.py click command, registered under python -m ci_orchestrator job. Backend selection goes through backends.load_backend(config) so Phase C can swap in remote drivers without touching the command. The legacy scripts/Invoke-CIJob.ps1 is replaced by a thin PS 5.1 shim that delegates to the Python CLI; tests/python/test_commands_job.py adds 13 cases covering Linux/Windows happy paths, override application, skip-artifact, and cleanup on every failure mode.
