Auto-detect agent author via OMNI_AUTHOR env var

When agents run via the pipeline, their task comment calls default to --author human because agents forget to pass --author agent:engineer.

Fix: auto-detect agent context via environment variable.

1. In Omni/Pipeline/Dev.hs spawnDev, set OMNI_AUTHOR=agent:engineer in the spawned process environment. 2. In Omni/Task.hs parseAuthor, check OMNI_AUTHOR env var as fallback when no --author flag is given:

• If --author is explicitly passed, use it (existing behavior)
• If not passed, check OMNI_AUTHOR env var
• If neither, default to Human (existing behavior)

This way agents running inside the pipeline automatically get correct attribution without needing to remember the flag.

Key files: Omni/Task.hs (parseAuthor, doComment), Omni/Pipeline/Dev.hs (spawnDev) Namespace: Omni/Task.hs