The bump-coana skill bumped package.json's version itself and wrote its own
`## [<version>]` changelog heading. Both belong to the release workflow, and the
skill's version of them caused real damage: headings for 1.1.160, a version that
never existed anywhere, and a v1.1.159 that shipped with no notes at all because
the hand-written heading had consumed the `[Unreleased]` block the release meant
to promote.

Point the skill at `[Unreleased]` instead, recreating that heading when the
previous release consumed it — having nowhere to put notes is what motivated the
invented headings in the first place.

Also separate the two failures behind writeManifestVersion's guard. A manifest
already holding the target version rewrites to itself, and `replaced === raw`
read that no-op as a missing field, so a release whose version the skill had
already written failed with "no top-level version line" against a manifest whose
version field was present and well-formed. Test for the field, then replace, and
let an already-correct manifest pass through.

* upgrading coana to version 15.10.25

* Fix

---------

Co-authored-by: socket-pr-bot[bot] <294242679+socket-pr-bot[bot]@users.noreply.github.com>
Co-authored-by: Oskar Haarklou Veileborg <ohv1020@hotmail.com>