Skill: Open a PR

A PR body is read in thirty seconds, before the diff. It answers a few questions and stops. Everything else lives in the commit messages, the spec, and the report CI posts.

The shape

.github/pull_request_template.md. Fill every heading; add none. Under ~250 words total.

## What is this about?
One or two sentences, plain words: the surface and the change.

## What problem does it solve?
The pain a person felt or the risk we carried. Not the mechanism.