Install Evergreen workflow

[mrjf]

Summary

• Replaces the previous custom .github/workflows/evergreen.md with a fresh Evergreen Agentic Workflow install.
• Vendors v1 Evergreen skills under .github/workflows/shared/skills/.
• Adds Evergreen repo policy and runtime components under .github/workflows/shared/evergreen/.
• Compiles .github/workflows/evergreen.lock.yml with gh aw compile evergreen.
• Creates approved Evergreen labels in the repository.

Install decisions

• Persistent opt-in label: evergreen.
• State labels: evergreen-ready, evergreen-blocked, evergreen-human-needed, evergreen-exhausted.
• Triggers: PR labeled/updated while labeled, scheduled scan every 15 minutes, manual dispatch by PR number.
• Merge policy: never directly merge; merge main into PR branches only through labeled PR branch repair work.
• CI gates: Test & Lint, Playground E2E (Playwright), Validate Python Examples, Build; OpenEvolve benchmark only for relevant Autoloop evolve PRs.
• Protected runtime edit policy: never edit README.md or .autoloop/programs/**; protect workflow/config files unless a human confirms.

Verification

• gh aw compile (succeeded; existing unrelated workflow warnings were emitted)
• gh aw compile evergreen (succeeded with 0 errors, 0 warnings)
• apm compile attempted, but this repo is not an APM project because no apm.yml exists.
• git diff --check

Repo setup applied

Created labels: evergreen, evergreen-ready, evergreen-blocked, evergreen-human-needed, evergreen-exhausted.

No new secrets/settings were needed; COPILOT_GITHUB_TOKEN and GH_AW_CI_TRIGGER_TOKEN already exist.

Note: the requested upstream INSTALL.md path was not present in githubnext/evergreen at install time; I followed the current upstream README/docs install notes and v1 workflow design instead.