feat(cron): expose durable execution identity to jobs

[cirwel]

Summary

• copy newly created execution IDs into the worker job envelope
• expose cron job and execution IDs through worker environment variables
• cover generated execution propagation and stale environment cleanup

Dependency

• stacked on fix(cron): harden runtime ownership, supervision, and recovery NousResearch/hermes-agent#75833, which introduces the execution ledger

Tests

• not run explicitly (per execution constraint)