chore(ci): re-enable pnpm cache

Runner cache backend is now reachable from the job container, so
`cache: pnpm` on setup-node works again. Reverts b77c097.

.gitea/workflows/ci.yml

@@ -21,15 +21,11 @@ jobs:
         with:
           version: 11.0.9
 
-      # NOTE: `cache: pnpm` is intentionally omitted. The Gitea cache server
-      # at 10.0.23.3:42951 is unreachable from the runner container, and each
-      # cache restore/save hangs ~4m40s on TCP timeout before failing. With
-      # caching off, total CI time is ~45s. Re-enable once the act_runner
-      # cache backend is reachable from inside the job container.
       - name: Setup Node
         uses: actions/setup-node@v4
         with:
           node-version: 22
+          cache: pnpm
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile