Write PR Description

Turn the current branch into a pull request a reviewer can follow without opening the diff.

The branch diff is the only authority for what the PR changed. Everything else — the sections, the checklist — comes from the target repository, never from memory.

Draft mode is the default: write the description and print it. Create mode also opens the PR, and applies only when the user asked to open, create or raise it. If they did not, say so and stop before Step 6.

The shape of a finished description is in references/example.md.

Scope

Read the branch, write the description, and in create mode push the current branch and open the PR.