fix(ci): make playwright blob report filenames unique per mongodb-version

The blob reporter names files by project + shard only (e.g.
report-chromium-guest-mode-1.zip), without the mongodb-version. report-playwright
downloads every blob-report-* artifact into one directory with
`download-artifact merge-multiple`, so the mongodb 6.0 and 8.0 jobs emitted
identical filenames that race during download and corrupt the zip, breaking
`playwright merge-reports` ("invalid central directory file header signature").

Prefix the mongodb-version to each blob filename before upload so every file is
unique across the whole matrix. Verified locally: merge-reports succeeds on all
12 uniquely-named blobs and produces a valid HTML report.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/reusable-app-prod.yml

@@ -348,6 +348,20 @@ jobs:
         MONGO_URI: mongodb://localhost:${{ job.services.mongodb.ports['27017'] }}/growi-playwright-guest-mode
         ELASTICSEARCH_URI: http://localhost:9200/growi
 
+    # The blob reporter names files by project + shard only (e.g.
+    # report-chromium-guest-mode-1.zip), without the mongodb-version. report-playwright
+    # downloads every blob-report-* artifact into one directory with merge-multiple,
+    # so the 6.0 and 8.0 jobs would emit identical filenames that race and corrupt the
+    # zip. Prefix the mongodb-version to keep them unique across the whole matrix.
+    - name: Make blob report filenames unique across the matrix
+      if: always()
+      run: |
+        cd apps/app/blob-report 2>/dev/null || exit 0
+        for f in *.zip; do
+          [ -e "$f" ] || continue
+          mv "$f" "mongo${{ matrix.mongodb-version }}-$f"
+        done
+
     - name: Generate shard ID
       id: shard-id
       if: always()