refactor(#1170): remove hand-maintained INVENTORY count scalars (#1179)

* refactor(#1170): remove hand-maintained INVENTORY count scalars

The `(N shipped)` heading counts in docs/INVENTORY.md were absolute
scalars that collided silently on merge: two branches each bumping the
same integer to N+1 produced a clean git merge whose value the merged
filesystem (N+2) contradicted, hard-failing inventory-counts.test.cjs on
the CI merge commit across all platforms (DEFECT.INVENTORY-MERGE-UNDERCOUNT).

- Strip the six `(N shipped)` heading counts + the two prose footnote
  counts; repoint the intro to INVENTORY-MANIFEST.json as the registry.
- Drop the decorative `generated` date from the manifest + its
  strip-before-compare branch in gen-inventory-manifest.cjs (it conflicted
  on cross-day merges and is read by nothing).
- Delete inventory-counts.test.cjs (scalar-vs-disk gate, the collision
  source); its drift protection is subsumed by the merge-safe set-membership
  test inventory-manifest-sync.test.cjs, which stays as the sole gate.
- Add inventory-headings-countfree.test.cjs guard (fails if a count is
  re-added to a heading).
- Fix already-broken count-bearing cross-doc anchors to stable count-free
  slugs in ARCHITECTURE.md + multi-agent-orchestration.md.
- Retire the now-impossible DEFECT.INVENTORY-MERGE-UNDERCOUNT + obsolete
  RULESET.DOC-CONSISTENCY in CONTEXT.md; de-count DEFECT.INVENTORY-DRIFT;
  correct stale MANIFEST-CANONICAL-KEY (all six families canonical).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#1170): backfill changeset PR number (#1179)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

scripts/gen-inventory-manifest.cjs

@@ -61,7 +61,7 @@ const FAMILIES = [
 ];
 
 function buildManifest() {
-  const manifest = { generated: new Date().toISOString().slice(0, 10), families: {} };
+  const manifest = { families: {} };
   for (const { name, dir, filter, toName } of FAMILIES) {
     manifest.families[name] = fs
       .readdirSync(dir)
@@ -78,9 +78,6 @@ function main() {
   if (flag === '--check') {
     const committed = JSON.parse(fs.readFileSync(MANIFEST_PATH, 'utf8'));
     const live = buildManifest();
-    // Strip the generated date for comparison
-    delete committed.generated;
-    delete live.generated;
     const committedStr = JSON.stringify(committed, null, 2);
     const liveStr = JSON.stringify(live, null, 2);
     if (committedStr !== liveStr) {