PROD-040 Add a PR evidence contract and automated validation

[rndrntwrk]

Canonical source: docs/release/github-project-production-backlog.md

Epic: Repository Governance, Review Automation, And OSS Housekeeping

• ID: PROD-040
• Title: Add a PR evidence contract and automated validation
• Type: ci
• Priority: P1
• Scope: active
• Area: review
• Description: Require PRs to state what changed, why, how it was verified, and
  what evidence exists, then validate that contract automatically for
  launch-critical surfaces.
• Acceptance criteria:
  • PR template requires What, Why, How, Testing, Evidence, Risk,
    and Rollback
  • protocol, keeper, app, and workflow PRs must include concrete evidence such
    as test commands, screenshots, tx hashes, or artifact paths
  • CI flags incomplete PR bodies or missing evidence for critical change areas
• Dependencies: PROD-039
• Source docs: stage-a-browser-acceptance-matrix.md,
  stage-a-promotion-execution-ledger.md,
  external-audit-package-checklist.md,
  external benchmark: milady/.github/PULL_REQUEST_TEMPLATE.md
• Suggested owner: release
• Blocker class: quality-blocking