test: add ARNES self-tests and docs index

docs/README.md

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+# Docs index
+
+## Core docs
+- `../README.md` — framework overview
+- `../HOWTO.md` — quick start
+- `../HOWTO-FEATURE.md` — feature workflow
+- `../TEMPLATE.md` — how to adapt ARNES
+
+## Reference docs
+- `repository-layout.md` — repo structure and separation rules
+- `scripts-reference.md` — start/verify/ticket/publish/install scripts
+- `skeleton-manual.md` — default Skeleton UI notes
+
+## Harness source of truth
+- `../harness/agents.matrix.yml` — roles and edit boundaries
+- `../harness/workflow.stages.yml` — ordered workflow stages
+- `../harness/policies/` — governance, security, quality, language, model routing