feat(devenv): CL-to-standalone cutover tooling and migration e2e

[tt-cll]

Description

Devenv tooling that performs the CL-to-standalone cutover end to end, plus the e2e test proving identity preservation, and the operator procedure (docs/migration/cl-to-standalone.md).

• Cutover: read CSA key and find the JD record, export keys via the shared migration package (previous PR), stop the CL node, launch standalone verifiers/executors with [key_import], repoint the existing JD record at the verifier's CSA key (no duplicate entry), register the executor, flip the topology to standalone.
• Job specs are retargeted to the standalone envelope preserving externalJobID and the inner config verbatim.
• requireDisjointExecutorChains rejects the one unsafe shape (two executors sharing an account and a chain race nonces).
• TestE2EMigration_CLToStandalone added to the CL smoke workflow: messages verify/execute before and after the cutover, with signing address, transmitter address, and JD record asserted unchanged.

Testing

Unit tests for credential hydration, disjoint-chain enforcement, and spec retargeting (idempotent, unknown-key preserving). E2E runs in CI via migration.clnode.ci.profile.

Checklist

• Breaking changes documented in changelog (see changelog directory)
• Cross link related PRs (in this or other repositories)

---

_{Stack created with GitHub Stacks CLI • Give Feedback 💬}