Expands `.github/pull_request_template.md` to require a linked issue, a
high-level design (for large PRs), a structured Tests section (use cases,
unit + coverage %, backend/ingestion integration tests, Playwright, manual
steps), and a UI screen recording for any UI change. Adds a `/pr-checklist`
skill that walks the template, gathers evidence, and drafts the PR body
before opening via `gh pr create`.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>