Revert CORS fetch mode for Active Storage

CORS mode doesn't work with redirect-based Active Storage URLs
when the storage bucket uses wildcard Access-Control-Allow-Origin.
Relying on maxEntries alone until specific origin CORS is available.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/views/pwa/service_worker.js.erb

@@ -42,8 +42,7 @@ TurboOffline.addRule({
     maxAge: 60 * 60 * 24 * 7,
     networkTimeout: 2,
     maxEntrySize: 2 * 1024 * 1024, // 2MB covers about 95% of all Fizzy blobs
-    maxEntries: 500,
-    fetchOptions: { mode: "cors", credentials: "omit" }
+    maxEntries: 500
   })
 })