Backport a PR to a maintenance major branch

develop is the current major (v11). A change that also needs to ship on a still-maintained older major has to land on that major's branch too (v10 by default). This skill cherry-picks a merged develop PR onto that branch and opens a draft backport PR.

Inputs

• PR (required): the already-merged PR on develop to backport, given as either a full GitHub URL or a bare number. gh pr view accepts both, so pass whichever the user gave through unchanged; <PR> in the commands below is that value.
• Target major (optional, default v10): the maintenance branch to backport onto. Accept v10, 10, v9, etc. Normalize to a branch name like v10.

If no PR is given, ask for it. Do not guess.

Convention