fix(docs): correct claims the first fix round asserted without measuring

Why: two blind verifiers re-ran the five preceding commits and found four
defects of the same class this branch exists to close -- a confidently stated
measured claim that does not survive re-measurement -- this time inside the
fixes themselves.

- AGENTS.md:41 still carried both phrasings c68e864 reports having corrected.
  `grep -rn repo-defined` returned exactly one hit repo-wide: that line, in the
  file every session preloads. 4d336bb edited the line directly above it.
- ADR-0021 asserted twice, in the section justifying that no gate is added,
  that the ADR-0020 validators "never open an apm.yml". All three open and
  yaml.safe_load it (skill-size-check.sh:342, both validate.sh). The conclusion
  survives -- none reads the description: key, and their globs are SKILL.md and
  *.agent.md only -- but the stated mechanism is falsified by one grep.
- architecture.md said the ADR directory holds 20 numbered ADRs; c7ba3d2 made
  it 21, and c68e864 audited that file for exactly this class of stale count.
  The number is dropped rather than corrected: `ls docs/adr/` is already the
  index, so a count in prose is a second thing to maintain.
- gates.md's new three-verdict table said `-> name` promotes an unresolved
  target to ERROR. Reproduced with fixtures: NAME_HYPH (skill-size-check.sh:543)
  requires a hyphen, so `-> gitea-prs` is checked and `-> triage` is not
  extracted at all, and the unicode arrow is never recognised. The SUGGESTION
  text advises that spelling, so taking its advice can silence the finding. The
  gap is now documented as a defect; nothing covers it, since the one arrow case
  in test-adr0020-targets.sh happens to use a hyphenated target.

Implementation notes:
- AGENTS.md:48's coverage claim is shrunk rather than chased. Restoring six
  glossary entries did not make it true: 12 more sampled terms are undefined,
  three of them (trigger/capability/boundary clause) used inside CONTEXT.md
  itself. It now says CONTEXT.md is the glossary and is not exhaustive.
- CONTEXT.md's output profile and near-miss entries are corrected against their
  sources. The first stated a false exclusion -- .github/plugin/plugin.json IS
  apm-generated; only the marketplace mirror has no profile. The second
  inverted its source's referent: description-quality.md defines a near-miss as
  a query, not a sibling skill.
- The strict-mode message named jq, which no suite guards on (`command -v jq`
  appears nowhere in tests/), while omitting python3/PyYAML, which three do.
- README's git and gitea bullets now name git-workflow and gitea-workflow.
  ADR-0021 leaves README the only inventory and architecture.md now points at
  it, so the two bullets that were short had to be completed.
- ADR-0018's 2026-08-14 correction is marked superseded in place. It asserted
  machine state in the present tense that its own 2026-08-17 note retracts.
- ADR-0021's remaining errors: six files -> four (measured from de84d1b), the
  wiki description's length 114 -> 96 chars, the codex self-contradiction, the
  cost argument overstating bumps already owed for any skill addition, and two
  claims about files this branch went on to edit.
- The "15 of 17 suites" figure is restored where I had removed it: it is a dated
  record of one incident, not a live count, and four sites now describe it the
  same way.

Impact: 16/16 pre-push hooks pass, suite 24 passed 0 skipped 0 failed. No
behaviour change; every edit is prose or a comment.

Refs: #105

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TmFqzpuExLJv3m114XVE9w

CONTEXT.md

@@ -69,10 +69,10 @@ plugin's `.apm/` tree so hosts that convention-scan those paths discover the con
 _Avoid_: generated copy, duplicate tree
 
 **Output profile**:
-An `apm pack` target format for a generated manifest; apm has `claude`
+An `apm pack` target format for a generated *marketplace* manifest; apm has `claude`
 (`.claude-plugin/marketplace.json`) and `codex` (the differently-shaped
-`.agents/plugins/marketplace.json`) and none for Copilot CLI's legacy path, which a sync script
-mirrors instead. Mechanics: `docs/spec/architecture.md`.
+`.agents/plugins/marketplace.json`), and none for `.github/plugin/marketplace.json` (Copilot CLI's
+legacy path), which a sync script mirrors instead. Mechanics: `docs/spec/architecture.md`.
 _Avoid_: build target, export format
 
 **Plugin marketplace**:
@@ -160,8 +160,9 @@ The directory a gate resolves against — the nearest ancestor of the file being
 _Avoid_: repo root, project root
 
 **Near-miss**:
-A sibling skill or agent whose plausible queries share keywords with this one but need something
-different — the only thing a boundary clause should exclude.
+A query that shares keywords with this skill but needs a different one — and, by extension, the
+sibling that would wrongly answer it; boundary clauses exist to exclude genuine near-misses rather
+than to enumerate siblings. Detail: `skill-audit/references/description-quality.md`.
 _Avoid_: overlap, similar skill
 
 **Vacuous green**: