fix: keep the fixture evidence test about preservation, and stop scanning worktrees

The release-evidence test asserted that every artifact a candidate is assembled
from survives the copy, which quietly assumed the checkout had already run the
release chain. It holds in this repository and fails in a product repository
that has not, where `artifacts/performance/bundle.json` simply does not exist
yet — a fact about the checkout, not about the copier. It now asserts that
whatever release evidence is present is preserved, and that at least one thing
was, so it cannot pass by finding nothing to check.

Vitest also walked `.worktrees/`. A git worktree inside the repository is a
different checkout of a different branch; running its tests against this
checkout's config produces failures that belong to neither and cost real time
to attribute.

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

vitest.config.ts

@@ -11,6 +11,10 @@ export default defineConfig({
     exclude: [
       ...configDefaults.exclude,
       ".tmp/**",
+      // A git worktree inside the repository is a different checkout of a
+      // different branch. Running its tests against this checkout's config
+      // reports failures that belong to neither.
+      ".worktrees/**",
       "tests/fixtures/v8-coverage-counter-semantics/**",
     ],
     coverage: {