fix(#4460): strip realpath -m from Tier 1 in the test (Windows CI)

CI's test (windows-latest, shard 1/3) failed: --files=src/alpha.js
widened to all 5 files instead of staying at 1. Root-caused (not
assumed): this is the SAME pre-existing Tier-1 `realpath -m`
portability gap already documented as out-of-scope for this fix
(confirmed on macOS during manual verification) -- also real on
Windows CI. `-m` only changes behavior for a path that doesn't (yet)
exist; on a platform where it errors or behaves differently, every
--files entry gets misclassified as "outside the repository",
REVIEW_FILES stays empty, and the test ends up exercising the OUTER
`if [ ${#REVIEW_FILES[@]} -eq 0 ]` full-diff fallback instead of ever
reaching the elif this fix's own gate lives on.

Fixed in the TEST only (code-review.md's Tier 1 is untouched -- this
gap is real, pre-existing, and out of #4460's scope per cr-2). Strip
`-m` from the extracted Tier 1 fence before running it: every path in
these fixtures already exists, so `-m` is a behavioral no-op here, and
this makes the test exercise Tier 3's gate (the actual subject of this
fix) on every platform gsd-test runs on. Manually re-verified both
cases locally before re-pushing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/code-review-tier3-files-override-scoping.test.cjs

@@ -102,7 +102,18 @@ function buildFixture(tmpDir) {
  */
 function runTiers(tmpDir, { filesOverride, seedReviewFiles = [] }) {
   const content = fs.readFileSync(WORKFLOW_PATH, 'utf-8');
-  const tier1 = extractFirstBashBlockAfter(content, '**Tier 1 — --files override', '**Tier 2 —');
+  // #4460 CI finding: Tier 1's `realpath -m` is a pre-existing, out-of-scope
+  // portability gap (BSD/macOS realpath has no -m; confirmed CI-reproducible
+  // on Windows too, where it likewise makes every --files entry look "outside
+  // the repository" and REVIEW_FILES stays empty, tripping the OUTER `if
+  // [ ${#REVIEW_FILES[@]} -eq 0 ]` fallback instead of exercising the gated
+  // elif this test targets). Not this fix's concern (see #4460's review
+  // notes) and every path in these fixtures already exists, so `-m` (which
+  // only changes behavior for a MISSING path) is a no-op here — stripped so
+  // this test exercises Tier 3's gate on every platform gsd-test runs on,
+  // not Tier 1's realpath compatibility.
+  const tier1 = extractFirstBashBlockAfter(content, '**Tier 1 — --files override', '**Tier 2 —')
+    .replace(/\brealpath -m\b/, 'realpath');
   const tier3 = extractFirstBashBlockAfter(content, '**Tier 3 — Git diff fallback', '**Post-processing');
 
   const filesArrayInit = filesOverride