perf(ci): add pnpm caching to storybook workflow

- Setup pnpm before setup-node so caching can detect it
- Enable node cache for pnpm in setup-node action
- Add explicit pnpm store caching with actions/cache@v4
- Key based on pnpm-lock.yaml hash for cache invalidation

This should dramatically speed up subsequent builds by reusing
the pnpm store instead of downloading 2563 packages each time.

.gitea/workflows/deploy-storybook.yml

@@ -22,13 +22,26 @@ jobs:
         with:
           fetch-depth: 0
 
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
           node-version: "20"
+          cache: 'pnpm'
 
-      - name: Setup pnpm
-        uses: pnpm/action-setup@v4
+      - name: Get pnpm store directory
+        shell: bash
+        run: echo "STORE_PATH=$(pnpm store path --silent)" >> $GITHUB_ENV
+
+      - name: Cache pnpm store
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.STORE_PATH }}
+          key: pnpm-store-${{ hashFiles('**/pnpm-lock.yaml') }}
+          restore-keys: |
+            pnpm-store-
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile