docs: adopt docs-template/ skeleton (architecture/usage/contributing/troubleshooting + ADR) (#11)

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.

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

Author: hyperpolymath