Close a GitHub milestone and carry unfinished work forward

**Objective:** Close the milestone titled `{milestone-title}` in `{repository}`, first moving any still-open issues to the milestone titled `{next-milestone-title}` when it is given, all with the user's confirmation.

**Step 1: Resolve the milestones**

Call `github-get-milestone` with company `{repository}` and title `{milestone-title}`, and keep its milestone-number, state, open-issues and closed-issues. If `{next-milestone-title}` is given, call `github-get-milestone` again with that title and keep its milestone-number.

**Step 2: List the unfinished work**

Call `github-get-issue` with company `{repository}`, milestone-title `{milestone-title}` and status `open`. List each issue-number, title and assignee.

**Step 3: Confirm the plan**

Show the user the milestone summary, the open issues, and the plan:

* move each open issue to `{next-milestone-title}`, or
* if no next milestone was given, leave the open issues where they are and ask whether to close the milestone anyway.

Wait for confirmation. The user may exclude individual issues.

**Step 4: Apply**

* For each approved issue, call `github-update-issue` with issue-number and the next milestone's milestone-number only.
* Then call `github-update-milestone` once with the milestone's milestone-number and state `closed`.

Re-read with `github-get-milestone` and report the final state and counts.

**Rules & Guidelines:**

* Never close issues in this prompt; do not pass state to `github-update-issue`.
* Do NOT call `github-add-milestone`. If the next milestone does not exist, stop and tell the user to create it first.
* Do NOT change the milestone's title, description or due-date.

**Validation:**

* If `{milestone-title}` matches no milestone, or more than one, list what was found and stop.
* If the milestone is already closed, say so and stop.