feat: bootstrap he maintainer skill

he-maintainer/references/monorepo.md

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+# Monorepo Harness Notes
+
+Use this reference when the repository contains multiple apps, packages, crates, or services.
+
+## What to map clearly
+
+- workspace root vs package roots
+- shared libraries vs deployable apps
+- root-level commands vs package-level commands
+- ownership boundaries between packages
+
+## Common risks
+
+- commands at the root may not validate a specific package well
+- agents may edit shared packages when a local override is safer
+- build, lint, and test commands may vary by package manager and workspace tool
+
+## Good harness patterns
+
+- include a short workspace map
+- show how to run commands for one package
+- define allowed scope for a task
+- prefer targeted validation for the touched package first