Add CI workflow for CLI regression suite

[Zefan-Cai]

Summary

• add a minimal GitHub Actions workflow for the pure-CLI AutoR stack
• run Python syntax compilation and the CLI regression-oriented unittest suite on PRs and branch pushes
• add manager-level smoke coverage for a full 8-stage run, redo-stage resume, rollback-stage resume, stage-local refinement continuation, and abort handling using a deterministic scripted operator
• add CLI subprocess smoke coverage for new-run abort, resume-run latest, and invalid redo-stage/rollback-stage argument combinations
• keep this PR scoped to TODO 10 testing and CI only

Covered TODO

• Partially completes TODO 10: testing and CI

Validation

• python -m py_compile main.py src/.py tests/.py
• python -m unittest discover -s tests -v