[WS-2111]: Clean up sw.js

[LukasFrm]

Resolves JIRA: https://bbc.atlassian.net/browse/WS-2111

Summary

This PR improves the service worker’s stability and caching, ensuring:

• No uncaught “Failed to fetch” errors are thrown in offline mode.
• Fetch handlers always return a valid Response (or fallback) when network/cache lookups fail.
• Cached items are kept up to date, with obsolete entries removed.
• Specific asset paths (Frosted Promo, SmartTag, Reverb, PWA icons) are aligned with the current Next.js asset layout and analytics hosting.
• Offline PWA behaviour remains intact and reliable.

Code changes

Fetch error handling

• All code paths return either a valid Response or a defined offline/fallback Response (no uncaught Failed to fetch).

Cache cleanup

• Aligned cached URLs and patterns with the live asset paths.

Frosted Promo

• Updated the caching rule from the old Simorgh static path to the new Next.js chunk path:
  https://static.files.bbci.co.uk/ws/simorgh-assets/public/_next/static/chunks/frosted_promo.*\.js

Reverb script

• Updated the Reverb script caching rule from the old static Simorgh location to:
  https://mybbc-analytics.files.bbci.co.uk/reverb-client-js/reverb-3.10.2.js

Moment.js

• Removed the old Moment.js caching rule (/moment-lib+.*?.js$) as Moment is now bundled via Next.js and no longer requires explicit SW caching.

Testing

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[Copilot]

Pull request overview

Bumps the service worker version and adjusts caching/fetch handling to improve offline stability and align cacheable asset routes with the current hosting/layout.

Changes:

• Bumped SW version to v0.3.4.
• Updated CACHEABLE_FILES entries for Reverb and Frosted Promo to match current asset locations.
• Changed fetch handler fallbacks to return a 503 Response instead of throwing / falling through.

[jinidev]

Upgrade cacheName as well

[jinidev]

This is not properly cached as per Toby's findings
Refer :https://bbc-tpg.slack.com/archives/C08JHPZFCTT/p1769509652307959?thread_ts=1769509469.732389&cid=C08JHPZFCTT.
So fix for this is WIP?

[elvinasv]

I am wondering if we should keep the fetch(event.request); 🤔 Is it possible to end up in the situation where isPWADeviceOffline = true, but the user is actually back online and the request is not a in navigation mode (i.e. isNavigationMode = false?

Probably we could attempt to do a request and catch error if needed?

  fetch(event.request).catch(err => {
    return new Response('', { status: 503 });
  })

[elvinasv]

Would that be a default fallback browser's behavior? I think we might lose error context if we just return 503 with an empty string 🤔

Edit: Although that would only happen in the navigation mode, not all requests.