Resolve PR conflicts

Update the PR's own branch against its current base. This skill does not authorize merging the PR or retargeting it to another base.

Inspect and update

gh pr view <n> -R <owner/repo> --json state,headRefName,headRefOid,baseRefName,mergeable,isCrossRepository,maintainerCanModify

1. Confirm the PR is open and record its head SHA and base branch.
2. Work in a temporary worktree, preserving existing local edits.
3. Fetch the PR head and base from their actual repositories; record the base tip.
4. Confirm fork permissions and the destination remote before updating the PR branch.
5. Merge or rebase onto the fetched base according to the repository's guidance.