test(fixtures): add vite-kitchen fixture repo

Minimal Vite + React + TS + Tailwind app with a typed-props Button
component (the future react-docgen-typescript scan target), landed at
fixtures/ outside the pnpm workspace and turbo graph. Its dependencies
exist on paper only — the runner installs them after cloning (story 04);
no lockfile, never pnpm-installed here.

Ignore surfaces follow the docs/product/reference precedent: fallow,
root ESLint, prettier, and the coverage:diff ALLOWED_GLOBS all skip
fixtures/**.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

scripts/coverage/diff.test.mjs

@@ -314,6 +314,21 @@ describe("computeDiffCoverage", () => {
     assert.equal(result.summary.filesChanged, 3);
   });
 
+  test("skips fixtures/ files (fixture repos, walking-skeleton story 01)", () => {
+    const lcov = parseLcov(lcovText);
+    const diff = new Map([
+      // Standalone fixture apps served to tests as git remotes — never
+      // executed by vitest, never in any lcov
+      ["fixtures/vite-kitchen/src/components/Button.tsx", new Set([1, 2, 3])],
+      ["fixtures/vite-kitchen/src/main.tsx", new Set([1, 2])],
+      ["fixtures/vite-kitchen/vite.config.ts", new Set([1])],
+    ]);
+    const result = computeDiffCoverage(diff, lcov);
+    assert.equal(result.status, "pass");
+    assert.equal(result.summary.filesGated, 0);
+    assert.equal(result.summary.filesChanged, 3);
+  });
+
   test("end-to-end fixture: mixed pass/fail/skip/no-data", () => {
     const lcov = parseLcov(lcovText);
     const diff = parseGitDiff(diffText);