Hearth

Cut a Hearth beta or promote a beta to stable, following the release-train cadence in RELEASING.md. Use whenever the request is to "cut a beta", "promote (the) beta to stable", "release <version>", "open the next beta", or "ship stable". Handles the stable/beta two-manifest split, the beta-parity guard, cutting the release via a pushed tag OR via workflow_dispatch when tag pushes are blocked, and landing the store manifest on a protected main through a PR.