verctl 0.3.13

Stack-agnostic version PRs from Changesets-format fragments
Documentation
# Merge the Version PR automatically once required checks pass

## Why

In the seven days to 2026-10-12, 13 Version PRs were merged by hand across
the six ctl repositories: ctl-core 6, forkctl 4, verctl, qctl, and
yamled 1 each, and unixd 0.
Each had one commit and green checks, so the merge added a wait and a click
and no review.
All six repositories already allow auto-merge.

Queue row: VER-047.

## What Changes

1. `actions/version-pr` gains an `auto-merge` input, `false` by default.
2. With `auto-merge: true`, after opening or updating the Version PR, the
   action enables GitHub auto-merge on it as a squash. The subject is the PR
   title and number, and the body is the PR description.
3. The action refuses to enable auto-merge when the base branch has no
   required status check, because GitHub would then merge at once with no
   gate.
4. This repository's Version PR workflow does the same.

## Capabilities

### New Capabilities

- `version-pr-auto-merge`: opting the Version PR into auto-merge behind the
  base branch's required checks.

## Impact

1. `actions/version-pr/action.yml`, `.github/workflows/version-pr.yml`,
   `examples/workflows/version-pr.yml`, README, and the operator
   instructions. The operator skill has no Version PR section, so it does not
   change.
2. Consumers opt in per repository with one input, after requiring their CI
   checks on the default branch.