Archive Project Endpoint

Archive a whole project: cancel its queued cold emails, stop live campaigns to Paused, zero all budgets, autopilot off, hide it everywhere (is_active=false). The project-level analog of campaign archive — see api/app_auto_gtm/project_archive.py. Reversible via /unarchive (campaigns stay Paused and budgets stay $0 after restore). Idempotent: archiving an already-archived project is a no-op 200.