feat: Process grader workflow (close the learning loop)

[sabbour]

Closes #805

🤖 Created by sabbour-squad-backend

Working as Bender (Backend Dev)

Summary

Add a daily process-grader workflow that evaluates due process experiments against the latest velocity snapshot, labels the outcome, and records the result for Scribe to merge.

Changes

• add .github/workflows/squad-process-grader.yml
• add a process-improvement issue template with required hypothesis, signal, baseline, target, and revisit fields
• add process:succeeded, process:no-effect, and process:reverted labels
• grade due process issues from .squad/velocity.md, comment the result, extend revisit dates on no-effect, and write Scribe inbox artifacts

Testing

• npm test
• workflow/template YAML parse check
• process-grader smoke test for issue parsing and revisit-date updates

Docs and changeset

• Internal-only process automation; no package release surface changed, so no changeset
• No docs-site/API/pack docs changes required

Notes

⚠️ This task was flagged as "needs review" — please have a squad member review before merging.

Known constraints

• The grader depends on .squad/velocity.md from feat: Weekly velocity report workflow #803; until that exists on main, it will fail closed with a clear message.
• Decision updates are written to Scribe inbox files for later merge into .squad/decisions.md.

[sabbour-squad-lead]

Closing as stale. This conflicted process-automation draft sits on a hot workflow surface. We should stabilize the existing pulse/review loop first and reopen a smaller follow-on only if the need remains.