docs: adopt docs-template/ skeleton (architecture/usage/contributing/… (#22)

…troubleshooting + ADR)

Closes Row-2 Phase 2 of the 2026-05-26 estate tech-debt audit chain for
this repo. The 2026-05-26 documentation-debt audit
(hyperpolymath/standards#197) flagged this repo as MEDIUM doc-debt:
substantial top-level README but no docs/ tree.

This PR seeds docs/ with the canonical 4-section + ADR skeleton from
hyperpolymath/rsr-template-repo#75:
  - docs/architecture.adoc   (system overview, components, invariants)
  - docs/usage.adoc          (consumer perspective)
  - docs/contributing.adoc   (developer perspective)
  - docs/troubleshooting.adoc (FAQ-style)
  - docs/decisions/0001-template.adoc (ADR template)

Placeholders ({{PROJECT_NAME}}, etc.) have been substituted to this
repo's actual values. The skeleton structure is canonical; the
substantive content is owed to the maintainer.

<!--
SPDX-License-Identifier: CC-BY-SA-4.0
Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
-->
## Summary

<!-- What does this PR do, and why? -->

Closes #

## Type of change

- [ ] 🐛 Bug fix (non-breaking change that fixes an issue)
- [ ] ✨ New feature (non-breaking change that adds functionality)
- [ ] 💥 Breaking change (would change existing behaviour)
- [ ] 🕳️ Soundness fix (fixes a checker/proof false-negative)
- [ ] 📖 Documentation
- [ ] 🧹 Refactor / tech debt (behaviour-preserving)
- [ ] ⚡ Performance
- [ ] 🔧 Build / CI / tooling

## How has this been verified?

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report?
     Don't cite a status doc — cite the command and its output. -->

## Checklist

- [ ] My commits are **signed** (`git commit -S`).
- [ ] I ran the project's own checks/tests locally and they pass.
- [ ] New files carry the correct `SPDX-License-Identifier` (code/config
`MPL-2.0`,
      prose `CC-BY-SA-4.0`); I did not relicense existing files.
- [ ] Docs are updated, and no public claim now overstates what the code
does.
- [ ] I have not introduced a soundness hole (or I have flagged where I
might have).

## Notes for reviewers

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath