ci(windows): cache bun installs; run the curated suite, not a hand list

- actions/cache on ~/.bun/install/cache keyed on bun.lock (install was
  35-45s of both 55-64s jobs, all network) and Bun pinned to 1.3.13 to
  match the other lanes.
- windows-free-tests now runs `bun run test:windows` (the runner's
  --windows-only curation) instead of a hand-listed 13-file subset that
  had drifted from the registry it sampled. POSIX-bound tests get
  excluded in ONE place (the curation patterns), not two.

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

.github/workflows/windows-setup-e2e.yml

@@ -39,7 +39,14 @@ jobs:
 
       - uses: oven-sh/setup-bun@v1
         with:
-          bun-version: latest
+          bun-version: 1.3.13
+
+      # Same lockfile-keyed install cache as windows-free-tests.yml (install
+      # was 45s of a 64s job, all network).
+      - uses: actions/cache@v4
+        with:
+          path: ~/.bun/install/cache
+          key: windows-bun-${{ hashFiles('bun.lock') }}
 
       - name: Configure git identity
         run: |