test(okf): add running n-way per-file parity gate + adversarial corpus (STEG 3)

Make OKF §3 checker parity a RUNNING per-file red/green signal instead of a
stale one-shot claim. The catalog and okr checkers provably diverge on the same
input (catalog walks everything + no BOM/CRLF norm; okr skips innboks/dot-dirs +
normalizes); this gate turns that divergence into a monitored, tested fact.

- scripts/check-okf-parity.mjs: n-way runner, zero-dep. Normalizes each impl's
  existing checkBundle(root) return to {conceptCount, untyped[], okfVersion} and
  compares per file over default read-mode. Impl registry is availability-guarded
  so a catalog-only checkout degrades gracefully; a documented subprocess seam
  awaits llm-ingestion-okf's Python checker (fase 2) + Node port (fase 4).
- test/okf-parity-corpus/: committed byte-exact adversarial corpus + manifest.
  Red-proof fixtures (expected: diverge) the gate MUST go red on — byte axis
  (BOM+CRLF) and tree axis (innboks, dot-dir) each carry one; canon = both.
  .gitattributes -text pins the BOM/CRLF bytes. Green fixtures pin agreement
  incl. a SHARED gap (both descend into node_modules).
- check-okf-parity.test.mjs: 8/8. Corpus assertions + byte-tracking red-proof +
  runtime-materialized symlink/NFC-NFD meta-tests + graceful-skip seam.

Honest scope: only 2 impls expose a runnable per-file checker today, so the gate
runs 2-way and is architected n-way — no faked third impl, no cross-repo code.
spec §7 + log.md updated (no self-certified parity; fixes stay upstream-first).

Verified: parity 8/8, CLI exit 0; regression 33/33; check-versions 10 OK.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NeK9hkxrU9wFPBYGYnSV1V

test/okf-parity-corpus/red-tree-dotdir/.hidden/untyped.md

@@ -0,0 +1,4 @@
+---
+title: hidden untyped
+---
+# no type

test/okf-parity-corpus/red-tree-dotdir/index.md

@@ -0,0 +1,3 @@
+okf_version: 0.1
+
+# Bundle root

test/okf-parity-corpus/red-tree-dotdir/typed.md

@@ -0,0 +1,8 @@
+---
+type: Note
+title: A concept
+description: A typed concept file.
+resource: about
+timestamp: 2026-07-23
+---
+# Note