Link a GitHub Issue + Linear Ticket on a PR

Appends a Sentry-style #### Issues block to a PR description, referencing both the GitHub issue and the Linear ticket pulled from the issue's linear-linkback comment.

Inputs

• <issue-url> — GitHub issue URL like https://github.com/<owner>/<repo>/issues/<n>. Issue number alone is fine if the PR is in the same repo.
• (optional) <pr-number> — defaults to the open PR for the current branch.

Steps

1. Resolve the PR number — skip if user supplied one:

   gh pr view --json number,body -q '.number'
   

   If no PR exists on the branch, stop and tell the user.