fix(release): pass the approved plan verbatim; bare milestone titles @osterman (#3644)

• atmos release cut now uses Starlark’s exec.run to pass RELEASE_APPROVED_PLAN to go tool mage release:cut without templating the approved plan, so release notes containing template syntax such as {{ ... }} do not cause the cut to fail after confirmation.
• Release milestones created by milestones ensure and milestones create now use bare version titles such as 1.236.0, while tags retain the v prefix; existing v-prefixed milestone titles remain supported.