Enable Vercel deploy previews on pull requests

.github/workflows/CI.yaml

@@ -1,16 +1,27 @@
 name: Vercel Preview Deployment
+
+on:
+  workflow_dispatch:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
 env:
   VERCEL_ORG_ID: ${{ secrets.VERCEL_ORG_ID }}
   VERCEL_PROJECT_ID: ${{ secrets.VERCEL_PROJECT_ID }}
-on:
-  workflow_dispatch:
-  # Uncomment when vercel project setup
-  # push:
-  #   branches-ignore:
-  #     - main
+
+concurrency:
+  group: preview-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   Deploy-Preview:
     runs-on: ubuntu-latest
+    if: >-
+      github.event_name == 'workflow_dispatch' ||
+      github.event.pull_request.head.repo.full_name == github.repository
+    permissions:
+      contents: read
+      pull-requests: write
     steps:
       - uses: actions/checkout@v5
 
@@ -29,4 +40,18 @@ jobs:
         run: vercel build --token=${{ secrets.VERCEL_TOKEN }}
 
       - name: Deploy Project Artifacts to Vercel
-        run: vercel deploy --prebuilt --token=${{ secrets.VERCEL_TOKEN }}
+        id: deploy
+        run: |
+          url=$(vercel deploy --prebuilt --token=${{ secrets.VERCEL_TOKEN }} | tail -n1)
+          echo "url=$url" >> "$GITHUB_OUTPUT"
+
+      - name: Comment the preview URL on the pull request
+        if: github.event_name == 'pull_request'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          URL: ${{ steps.deploy.outputs.url }}
+        run: |
+          gh pr comment ${{ github.event.pull_request.number }} \
+            --repo ${{ github.repository }} \
+            --edit-last --create-if-none \
+            --body "Preview deployment: $URL"