Releases now land via a PR from an ad-hoc branch rather than a commit
pushed straight to the target, so `bump.ts` keyed the ledger off the
ephemeral PR branch and scattered each release into its own file instead
of accumulating in `main.txt`.
Recover the target from a `release-pr/<target>` branch name, add a
manually-dispatched workflow that creates such a PR, and drop the
accumulated per-PR ledger files (verified inert: no overlap with pending
changesets, no live branch reintroduces a released changeset on merge).
Zoltan Kochan
69354b288f