pr-explainer

Build a self-contained HTML review aid at .pr-review/{branch}.html that teaches a reviewer what a PR changes and why — problem, system context, before/after flow, focused diffs, verification evidence, takeaway. Use when asked to explain a PR, help reviewers understand a complex change, or produce a review page for a branch. Do not use it as a substitute for review itself (/self-review) or instead of a PR description.