ci: re-enable actions cache now that the runner serves it

The Gitea Actions cache service now answers on 10.200.0.1:43513
(post nftables fix on the runner side). Turn `cache: true` and
`cache: pnpm` back on so setup-go/setup-node can use it for
cross-job tarball caching on top of the host-persistent caches we
already rely on.

The setup-* actions still tolerate the cache being unavailable, so
this is reversible to `cache: false` if the service goes away again.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/ui-test.yaml

@@ -37,11 +37,8 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: 22
-          # `cache: pnpm` pushes the pnpm store through the Gitea
-          # Actions cache service which is currently unreachable
-          # (192.168.0.222:43513 ETIMEDOUT). In host-mode the real
-          # store lives in ~/.local/share/pnpm and persists between
-          # jobs without any action plumbing.
+          cache: pnpm
+          cache-dependency-path: ui/pnpm-lock.yaml
 
       - name: Install npm dependencies
         working-directory: ui