Install staged Merge Steward

[mrjf]

Summary

• add a schema-validated merge-readiness contract derived from the trusted CI and repository rules on main
• classify the four checks already used by Evergreen as required on every head: Test & Lint, Playground E2E, Build, and Validate Python Examples
• classify OpenEvolve, Copilot setup, and Pages build/deploy as advisory evidence
• add a staged Agentic Workflow that reconciles PR, review, CI-completion, manual, and scheduled events
• retain read-only agent permissions and preview-only safe outputs

This installation deliberately does not dispatch CI, update PR branches, require new human reviews, or enable auto-merge. Those capabilities can be activated independently after the staged behavior is reviewed.

The full gh aw compile also resolves and pins github/gh-aw-actions/setup@v0.87.10 in the existing generated lockfiles and shared actions lock.

Validation

• gh aw validate .github/workflows/merge-steward.md --no-check-update
• gh aw compile --no-check-update
• JSON Schema validation of .github/merge-steward.yml (8 classified jobs)
• verified the required set exactly matches the four checks configured in Evergreen
• git diff --check

apm compile was attempted from an isolated environment, but the available system Python 3.9 cannot run the current apm-cli dependency (typing.TypeGuard is unavailable). No APM-managed source files were changed.