fix(release): bump plugin.json and marketplace.json on tag-push releases

[arnaudlh]

Why

The release workflow's Commit version bump step is gated to workflow_dispatch only:

- name: Commit version bump (workflow_dispatch only)
  if: github.event_name == 'workflow_dispatch' && steps.bump.outputs.changed == 'true'

So when a release is created the normal way — by pushing a tag (git push origin vX.Y.Z), which is also what gh release create does — the bumped plugin.json and .github/plugin/marketplace.json are used in-process to build the VSIX but never committed back to main.

That's why after v0.0.2 and v0.0.3 shipped, main was still pinned at 0.0.1 and CHANGELOG.md didn't exist. The downstream Update CHANGELOG.md on main step likely also opened a changelog/<tag> PR each time that nobody merged.

The drift on main is being corrected separately in #123.

What

Rework the post-release main-update step so it lands the version bump and the changelog entry in a single commit on main, regardless of whether the release was triggered by tag-push or workflow_dispatch.

• Rename: Update CHANGELOG.md on main → Bump version files and update CHANGELOG.md on main
• After git checkout -B changelog-update origin/main, re-apply the same jq bumps used by the earlier Bump plugin.json and marketplace.json step against the freshly-checked-out main tree.
• Extend the diff-skip check, git add, and commit message to cover plugin.json + .github/plugin/marketplace.json.
• Rename the fallback PR branch from changelog/<tag> to release/<tag> and broaden its title + body.
• Behaviour preserved:
  • workflow_dispatch flow continues to commit the bump + tag from the dispatching branch before VSIX assembly (the earlier step is untouched). The new step is idempotent there — git diff --quiet skips when there's nothing to land.
  • Prereleases (-rc.x etc.) remain skipped on the main-bump.
  • VSIX assembly path is unchanged.

Validation

$ actionlint .github/workflows/git-ape-release.yml
$ echo $?
0

Full end-to-end validation needs a tag-push release; the natural next opportunity is the next time we cut a tag.