gh-action: setup pnpm via action

.github/workflows/release.yml

@@ -33,6 +33,11 @@ jobs:
         with:
           fetch-depth: 0
 
+      # setup pnpm
+      - uses: pnpm/action-setup@v4
+        with:
+          version: latest
+
       # install latest node
       - name: Set up Node.js
         uses: actions/setup-node@v5
@@ -44,7 +49,6 @@ jobs:
       # build sveltekit frontend
       - name: Build frontend
         run: |
-          npm i -g pnpm
           pnpm --prefix=./frontend i
           PUBLIC_VERSION=${GITHUB_REF##*/} pnpm --prefix=./frontend run build
           cp -r ./frontend/build/* ./backend/pb_public/