feat: bootstrap enrollment for Central and Pilot

[prathameshkurunkar7]

feat(atlas): bootstrap-token enrollment (seed, don't inject, the credential)

Provisioning now hands the bench a short-lived enrollment token instead of the durable credential.

• create_site / deploy_site / guest deploy-site.py thread a single-use bootstrap_token (was central_auth_token); the bench runs bench enroll to mint its own long-lived credential. The durable secret is never written during provisioning.
• Retires provision.regenerate_vm_login — bench-open no longer re-mints a login via Atlas (Central signs the SID, the bench verifies it against the JWKS). Site-login is unchanged.

What's next (separate PR — not in scope here)

Enrollment still rides the post-boot deploy SSH, so this doesn't yet remove the boot wait. Follow-up:

1. Deliver the seed as VM create-time metadata (cloud-init / Firecracker MMDS) instead of over SSH — the seam already exists (ProvisionRequest.cloud_init, currently unused).
2. Golden image: ship a first-boot bench enroll unit that reads the seed from the canonical path; then drop the SSH bench enroll from deploy-site.py.
3. Then: a pre-warm bench pool (claim a booted, already-enrolled bench at signup) — the real signup-latency win, its own initiative.

Foundation is already in place on the Pilot side (bench enroll --seed-file + canonical-path auto-read);

Related PRs - Central Pilot

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the rename is complete and consistent, and no call sites were missed.

All central_auth_token references are gone (only a comment remains), the argparse attribute name matches the dataclass field, and the enrollment flow is guarded by the same condition as before. No logic changes beyond the deliberate credential-handoff redesign.

No files require special attention.

_{Reviews (4): Last reviewed commit: "refactor: fix pre-commit checks" | Re-trigger Greptile}