Skip Preview workflow for Dependabot PRs (#144)

Dependabot-triggered runs read from the Dependabot secrets store, which
is empty, so the Google Cloud auth step receives an empty credential and
fails. Skip the preview job for Dependabot; CI still validates those PRs.

Also guard the PR comment step so it doesn't post 'Failed to read
preview output' when the preview step never ran.

Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/preview.yml

@@ -16,8 +16,8 @@ jobs:
   preview:
     name: Preview Changes
     runs-on: ubuntu-latest
-    # Skip preview for fork PRs - they don't have access to secrets
+    # Skip preview for fork PRs and Dependabot - they don't have access to Actions secrets
-    if: github.event.pull_request.head.repo.full_name == github.repository
+    if: github.event.pull_request.head.repo.full_name == github.repository && github.actor != 'dependabot[bot]'
     environment: production
     steps:
       - name: Checkout code
@@ -101,7 +101,7 @@ jobs:
           exit $PREVIEW_EXIT_CODE
 
       - name: Comment on PR
-        if: always()
+        if: always() && steps.preview.conclusion != 'skipped'
         uses: actions/github-script@v7
         with:
           script: |