Chrome warns that an empty fetch listener adds navigation overhead.
Removed the handler entirely — a registered SW without a fetch handler
still satisfies Chrome's PWA installability requirement since v112.
Add a minimal sw.js with an empty fetch handler — required by Chrome
for the PWA install prompt to appear. Register it at the bottom of
dashboard.html with a silent catch. Add "scope": "." to the manifest.
Register sw.js in web_accessible_resources so Chrome can fetch it from
the extension origin.
Raven Scott