ci: add staging deploy job for PRs

Deploy to vp-setup-staging on pull requests after tests pass, using the
project config from .void/project.json. Comments on the PR with the
staging preview URL after successful deployment.

Author: fengmk2

.github/workflows/ci.yml

@@ -5,6 +5,9 @@ on:
   pull_request:
     branches: [main]
 
+permissions:
+  pull-requests: write
+
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -19,3 +22,29 @@ jobs:
       - run: vp check
       - run: vp build
       - run: vp test
+
+  staging-deploy:
+    needs: test
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: voidzero-dev/setup-vp@v1
+        with:
+          cache: true
+          registry-url: https://npm.pkg.github.com
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NODE_AUTH_TOKEN }}
+      - run: vpx void deploy
+        env:
+          VOID_TOKEN: ${{ secrets.VOID_TOKEN }}
+      - name: Comment on PR
+        uses: actions/github-script@v7
+        with:
+          script: |
+            github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              body: '✅ Staging deployment successful!\n\nPreview: https://vp-setup-staging.void.app/'
+            })