feat(#4593): add a macOS-specific conformance tier, final phase of epic #4589 (#4607)

test-conformance's macos-latest leg (Phase 2, #4591) has been running the
same 546-file, Windows-oriented conformance-tier list as windows-latest --
built from signals like windows-shell-token/windows-env-var that have
nothing to do with macOS. Issue #4593 asked for macOS coverage sized to
its own evidence-backed surface (zsh dispatch, case-sensitivity, darwin-
specific behavior) instead.

Issue #4593 was filed before Phase 5 (#4603) existed and referenced
updating test-full's macOS legs -- that job is gone. Corrected the issue's
body before any code was touched: the "shrink from full replay" half of
the original ask was already done by Phase 5; what remained was narrowing
the still-Windows-oriented tier macOS was inheriting.

Two design assumptions were measured and rejected before accepting a
design (documented in docs/adr/4593-macos-conformance-tier-architecture.md):
- Reusing the general tier's signals minus its 3 Windows-specific
  categories barely narrows anything (546 -> 424, 78% retained) -- most
  files match multiple signals and only need one to survive exclusion.
- A standalone CRLF/autocrlf signal, despite the issue naming
  "CRLF-checkout behavior": even narrowed to /\bCRLF\b|autocrlf/i it hit
  143/930 files. Root cause: CRLF is primarily a Windows checkout concern
  in this codebase (ADR-1703 files it under DEFECT.WINDOWS-TEST-
  PORTABILITY), so the signal was really re-selecting Windows-relevant
  files already covered by the general tier, not narrowing macOS
  specifically.

Built 5 new, genuinely macOS-specific signals instead: darwin-literal
(darwin alone, not the general tier's win32-OR-darwin), zsh-dispatch,
case-sensitivity, plus chmod-mode-bit and symlink-keyword reused verbatim
from the general tier (genuinely Unix-relevant, not Windows-motivated).
Measured against the real tree: 196 of 930 eligible unit-suite files
(21%), versus the general tier's 546 (59%) -- a real, evidence-backed
narrowing.

scripts/gen-platform-conformance-tier.cjs gains classifyMacosContent/
classifyMacosTree/renderMacosGeneratedFile and a --target windows
(default, unchanged)/--target macos CLI flag, so the same generator
produces two independent, gated outputs rather than needing a second
script. New committed output: scripts/lib/macos-conformance-tier.
generated.cjs. .github/workflows/test.yml's test-conformance job: only
the macos-latest leg's file-list source changes; windows-latest is
byte-for-byte untouched. New shipped-file ripples handled proactively
(19 install-tree fixtures regenerated, bin/install.js registered).

An isolated code-review pass found one real defect: the ADR's per-
category count table had drifted by 1 (zsh-dispatch, case-sensitivity)
because the new test file's own fixture strings joined the tree it
classifies after the table was authored -- fixed, with the union total
(196, what CI actually gates on) confirmed unaffected. An isolated
security-review pass found no qualifying findings.

The ADR also records an explicit requirement for any future widening
proposal: check whether the motivating regression is already covered by
Phase 1's no-rendered-text-length-assert lint rule (#4590) before
re-proposing full macOS/Linux parity, since that is exactly what #4421's
root cause was (a rendered-text-length assertion, not a real behavioral
divergence).

Co-authored-by: sim <sim@local>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

package.json

@@ -110,7 +110,7 @@
     "gen:registry": "node scripts/gen-registry.cjs --write",
     "gen:install-tree": "node scripts/gen-install-tree-fixtures.cjs",
     "gen:section-manifest": "node scripts/gen-section-manifest.cjs --write",
-    "regen:derived": "npm run build && npm run gen:registry && node scripts/gen-adr-index.cjs --write && node scripts/gen-features.cjs --write && node scripts/gen-capability-matrix.cjs --write && node scripts/gen-inventory-manifest.cjs --write && node scripts/gen-context-index.cjs --write && node scripts/gen-state-md-docs.cjs --write && npm run gen:section-manifest && node scripts/sync-manifest-versions.cjs && npm run gen:install-tree && node scripts/gen-scripts-cli-exit.cjs --write && node scripts/gen-hooks-cli-exit.cjs --write && node scripts/gen-exit-code-registry.cjs --write && node scripts/gen-exit-code-docs.cjs --write && node scripts/gen-platform-conformance-tier.cjs --write",
+    "regen:derived": "npm run build && npm run gen:registry && node scripts/gen-adr-index.cjs --write && node scripts/gen-features.cjs --write && node scripts/gen-capability-matrix.cjs --write && node scripts/gen-inventory-manifest.cjs --write && node scripts/gen-context-index.cjs --write && node scripts/gen-state-md-docs.cjs --write && npm run gen:section-manifest && node scripts/sync-manifest-versions.cjs && npm run gen:install-tree && node scripts/gen-scripts-cli-exit.cjs --write && node scripts/gen-hooks-cli-exit.cjs --write && node scripts/gen-exit-code-registry.cjs --write && node scripts/gen-exit-code-docs.cjs --write && node scripts/gen-platform-conformance-tier.cjs --write && node scripts/gen-platform-conformance-tier.cjs --target macos --write",
     "validate:registry": "node scripts/validate-registry.cjs",
     "prepack": "npm run build:lib",
     "prepare": "npm run build:lib",
@@ -132,7 +132,7 @@
     "lint:test-file-count": "node scripts/lint-test-file-count.cjs",
     "lint:pr-checks": "node scripts/lint-pr-check-project-dir.cjs",
     "lint:changeset": "node scripts/changeset/lint.cjs",
-    "lint:generated-sync": "node scripts/gen-capability-registry.cjs --check && node scripts/gen-loop-host-contract.cjs --check && node scripts/gen-capability-matrix.cjs --check && node scripts/sync-manifest-versions.cjs --check && node scripts/gen-inventory-manifest.cjs --check && node scripts/generate-package-identity.cjs --check && node scripts/gen-plugin-skills.cjs --check && node scripts/gen-registry.cjs --check && node scripts/gen-adr-index.cjs --check && node scripts/gen-features.cjs --check && node scripts/check-glossary-refs.cjs --check && node scripts/lint-compiled-artifact-sync.cjs --check && node scripts/gen-context-index.cjs --check && node scripts/gen-section-manifest.cjs --check && node scripts/gen-health-docs.cjs --check && node scripts/gen-state-md-docs.cjs --check && node scripts/gen-scripts-cli-exit.cjs --check && node scripts/gen-hooks-cli-exit.cjs --check && node scripts/gen-exit-code-registry.cjs --check && node scripts/gen-exit-code-docs.cjs --check && node scripts/gen-platform-conformance-tier.cjs --check",
+    "lint:generated-sync": "node scripts/gen-capability-registry.cjs --check && node scripts/gen-loop-host-contract.cjs --check && node scripts/gen-capability-matrix.cjs --check && node scripts/sync-manifest-versions.cjs --check && node scripts/gen-inventory-manifest.cjs --check && node scripts/generate-package-identity.cjs --check && node scripts/gen-plugin-skills.cjs --check && node scripts/gen-registry.cjs --check && node scripts/gen-adr-index.cjs --check && node scripts/gen-features.cjs --check && node scripts/check-glossary-refs.cjs --check && node scripts/lint-compiled-artifact-sync.cjs --check && node scripts/gen-context-index.cjs --check && node scripts/gen-section-manifest.cjs --check && node scripts/gen-health-docs.cjs --check && node scripts/gen-state-md-docs.cjs --check && node scripts/gen-scripts-cli-exit.cjs --check && node scripts/gen-hooks-cli-exit.cjs --check && node scripts/gen-exit-code-registry.cjs --check && node scripts/gen-exit-code-docs.cjs --check && node scripts/gen-platform-conformance-tier.cjs --check && node scripts/gen-platform-conformance-tier.cjs --target macos --check",
     "lint:docs": "node scripts/lint-docs-required.cjs",
     "lint:qa-smells": "node scripts/qa-smell-ratchet.cjs",
     "lint:legacy-name": "node scripts/lint-legacy-dir-name.cjs",