chore(tidy): T-3 — move loose root docs into the docs/ subtree (#365)

## Summary

Phase T-3 of the repo-tidy stack. Twelve loose root-level documents
migrated into the existing `docs/` subtree, plus two new subdirectories
where the existing taxonomy had no obvious home for the content. Root
drops from 17 loose `.md`/`.adoc` files to 5 (the
RSR-template-compatible minimum: README, CONTRIBUTING, CODE_OF_CONDUCT,
SECURITY, MAINTAINERS).

## Moves

| From (root) | To (docs/...) |
|---|---|
| `ABI-FFI-README.md` | `reference/ABI-FFI.md` |
| `ALPHA-1-RELEASE-NOTES.md` | `history/ALPHA-1-RELEASE-NOTES.md` |
| `BACKEND-ANALYSIS.md` | `architecture/BACKEND-ANALYSIS.md` |
| `BACKEND-IMPLEMENTATION.md` | `architecture/BACKEND-IMPLEMENTATION.md`
|
| `COMPILER-CAPABILITIES.md` | `reference/COMPILER-CAPABILITIES.md` |
| `EXPLAINME.adoc` | `EXPLAINME.adoc` |
| `KNOWN-ISSUES.md` | `KNOWN-ISSUES.md` |
| `LICENSING-GUIDE.md` | `governance/LICENSING-GUIDE.md` |
| `NAVIGATION.adoc` | `NAVIGATION.adoc` |
| `PROOF-NEEDS.md` | `PROOF-NEEDS.md` |
| `ROADMAP.adoc` | `ROADMAP.adoc` |
| `RSR_OUTLINE.adoc` | `standards/RSR-OUTLINE.adoc` |
| `SECURITY-SETUP.md` | `governance/SECURITY-SETUP.md` |

Two new subdirectories: `docs/architecture/` (compiler / backend
internals) and `docs/reference/` (technical reference).

## Cross-reference fixes (same PR — no broken links left behind)

- `docs/CAPABILITY-MATRIX.adoc` — authoritative-source caveat block now
points at the new paths.
- `docs/architecture/BACKEND-IMPLEMENTATION.md` — Related-Documentation
block rewritten with `../history/...` / `../ROADMAP.adoc` relatives.
- `CONTRIBUTING.md` — repo-layout block drops the moved `ROADMAP.adoc`
root entry; "skim before suggesting features" link now →
`docs/ROADMAP.adoc`.
- `docs/NAVIGATION.adoc` — every `link:docs/X` becomes `link:X` (it's
now in `docs/`); the Directory Tree Overview block rewritten to reflect
the current repo shape (drops the long-stale `.build/` and `STATE.scm`
entries that never existed; adds the new subdirs; mentions
`.well-known`, `.github`, `.machine_readable`).
- `tools/res-to-affine/{README.md, scanner.ml,
test/expected/sample.affine}` — the `raw-js` migration-guidance string
referenced `ABI-FFI-README.md`; updated to `docs/reference/ABI-FFI.md`.
Snapshot fixture updated by hand to match the scanner's new emitted
text.

## Out of scope (deliberate)

- `docs/history/TYPED-WASM-LEVEL-10-CLOSURE-2026-04-19.{adoc,a2ml}`
mention `KNOWN-ISSUES.md` in *historical past-tense* ("flipped to
RESOLVED") — those are session-note retrospectives, not navigation
links. Leaving them preserves the historical record.

## Test plan

- [ ] CI baseline preserved — no `.ml`/`.mli` files moved, so `dune
build`/`lint` behaviour unchanged from `main`'s current state.
- [ ] `grep -rl` for the moved filenames across `.md` / `.adoc` / `.ml`
/ `.mli` returns only the carve-outs noted above.
- [ ] Hypatia: no new findings; `unpinned_action` + TypeScript-exemption
hits unchanged from baseline.

## Stack

- ✅ T-1 (#359 merged) — AI manifest canonical name + TECH-DEBT restore
- ✅ T-2 (#360) — game-file deletion
- 🟡 **T-3 (this PR)** — root → docs/ reshuffle
- T-4 — `RSR_COMPLIANCE.adoc` + `STATE.scm` per RSR template
- T-5 — refresh `wiki/`
- T-6 — issue / PR triage

Phase 2c (#357) is on a separate branch and unaffected.

---
_Generated by [Claude
Code](https://claude.ai/code/session_01WNkH8UucP3PppG5R36kGcu)_

---------

Signed-off-by: hyperpolymath <6759885+hyperpolymath@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

CONTRIBUTING.md

@@ -50,7 +50,6 @@ affinescript/
 ├── LICENSE / LICENSES   # MIT OR AGPL-3.0-or-later
 ├── MAINTAINERS.adoc
 ├── README.adoc
-├── ROADMAP.adoc
 ├── SECURITY.md
 ├── dune-project
 └── justfile
@@ -76,7 +75,7 @@ affinescript/
 ### Suggesting Features
 
 **Before suggesting:**
-1. Skim [`ROADMAP.adoc`](ROADMAP.adoc) and `.machine_readable/6a2/STATE.a2ml`.
+1. Skim [`docs/ROADMAP.adoc`](docs/ROADMAP.adoc) and `.machine_readable/6a2/STATE.a2ml`.
 2. Search existing issues and discussions.
 
 **When suggesting:** use the [feature request template](.github/ISSUE_TEMPLATE/feature_request.md) and include:

NAVIGATION.adoc

@@ -10,8 +10,10 @@
 ====
 *This document is the single authoritative source for AffineScript feature
 readiness.* Where any other document (`README.adoc`,
-`BACKEND-IMPLEMENTATION.md`, `COMPILER-CAPABILITIES.md`,
-`ALPHA-1-RELEASE-NOTES.md`, `ROADMAP.adoc`, `.machine_readable/6a2/STATE.a2ml`)
+`docs/architecture/BACKEND-IMPLEMENTATION.md`,
+`docs/reference/COMPILER-CAPABILITIES.md`,
+`docs/history/ALPHA-1-RELEASE-NOTES.md`, `docs/ROADMAP.adoc`,
+`.machine_readable/6a2/STATE.a2ml`)
 disagrees with this matrix, *this matrix wins* and the other document is drift
 to be corrected. Reconstructed and verified 2026-05-19 against
 `origin/main`@dc5b817 with the compiler as oracle. Tracks issue