ci(deploy-preview): include capture script hash in prod-screenshots cache key

The cached production screenshots survive across runs. When the capture
script changes (settle waits, scrollbar handling, crop-vs-pad, etc.), a
new run's fresh preview captures are compared against prod screenshots
taken under the old algorithm, producing asymmetric phantom diffs.

Adding the script's content hash to the cache key auto-busts the cache
on any change to capture behavior, eliminating the need for manual cache
deletion after script updates.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: sserrata

.github/workflows/deploy-preview.yml

@@ -255,7 +255,12 @@ jobs:
         uses: actions/cache/restore@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:
           path: visual_diffs/prod
-          key: prod-screenshots-${{ steps.sitemap-hash.outputs.hash }}
+          # The capture script's content is part of the cache key so changes to
+          # capture behavior (settle waits, scrollbar handling, etc.) bust the
+          # cache automatically. Without this, cached prod screenshots taken
+          # under an older algorithm would be compared against fresh previews
+          # taken under a newer one, producing asymmetric phantom diffs.
+          key: prod-screenshots-${{ hashFiles('scripts/sitemap-visual-diff.ts') }}-${{ steps.sitemap-hash.outputs.hash }}
 
       - name: Run visual diff
         run: yarn ts-node scripts/sitemap-visual-diff.ts --preview-url "$PREVIEW_URL" --summary-file visual_diffs/results.json --concurrency 4 --paths "/tests/"