Summary

Add a visible parity and coverage report to the E2E parity comparison workflow so maintainers can see assertion conversion progress, scenario coverage, and known platform gaps directly from GitHub Actions.

Parent / Epic

Part of #3588.

Scope

• Render mapped / not-yet-converted / retired assertion counts from test/e2e/docs/parity-map.yaml.
• Include the scenario coverage matrix from the scenario runner metadata.
• Surface largest legacy assertion conversion gaps by entrypoint.
• Call out platform limitations, especially hosted macOS lacking Docker for full onboarding.
• Publish the report to the workflow step summary and retain it as an artifact.

Current PR

Draft PR: #3587

Acceptance Criteria

• E2E parity compare workflow publishes a Markdown report to $GITHUB_STEP_SUMMARY.
• Report artifact is uploaded with other .e2e/parity artifacts.
• Report uses “assertions not yet converted” language instead of “deferred signal”.
• Report explicitly identifies macOS full-onboarding limitation due to unavailable Docker.
• PR lands after the scenario live-execution PR fix(e2e): run scenario workflow for real #3493.