Scaffold the handbooks repo: scope, format convention, git-operations outline

Sibling store to halogen-workstation-roadmap's skills/ — instance-agnostic
reference material meant for KB admission, not for loading into context.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YKviBjJejufEUmryJ42tLT

README.md

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+# Handbooks
+
+Instance-agnostic reference material for coding agents — the verbose, citable kind that belongs in
+a retrieval store, not in a skill.
+
+## What goes here
+
+- Public standards, style guides, and conventions that apply regardless of which box or project is
+  running — general git operations, language style guides, CERT/MISRA-style rulebooks.
+- Long-form and specific. A handbook can be as detailed as it needs to be; nothing here is loaded
+  into a model's context wholesale, so length carries no per-turn tax.
+
+## What does not go here
+
+- **Anything specific to one machine or one project.** A local Gitea's branch-naming rule, this
+  box's PR checklist — that's instance-bound and belongs in that project's own KB corpus instead
+  (`kb-engineering` for [halogen](https://pi5-16.local/mikkeli/halogen-workstation-roadmap)).
+- **Short, prescriptive procedures achievable within a context window or two.** That's a skill, not
+  a handbook — it gets loaded, not retrieved. See `skills/` in the halogen-workstation-roadmap repo
+  for the sibling convention.
+- **The retrieval store itself.** This repo holds the source-of-truth markdown a human has vouched
+  for. The chunked, embedded index built from it is derived and rebuildable state — it lives beside
+  whichever KB is consuming it, never committed here.
+
+## Format
+
+One markdown file per topic at the repo root. Each file should stand as a single admittable
+document — the same shape a human vouches for at KB admission time.
+
+## Status
+
+Started 2026-08-21. First handbook: general git operations.