Fix scope issue where cachedResponse wasn't accessible in catch block.
Now if fetch fails, we first check if we have a cached response and
return it. If no cache exists, we let the error propagate so the
browser can handle it gracefully.
Add proper error handling to prevent uncaught promise rejections when
image fetches fail. If a fetch fails, try to return cached response,
or gracefully handle the error instead of letting it propagate as an
uncaught promise rejection.
Remove all console.log, console.warn, and console.error statements
that were added for debugging in article cache, service worker,
and image caching code.
With injectManifest strategy, the Service Worker needs to be built, so it's
not available in dev mode. To enable testing image caching in dev, we now:
1. Created public/sw-dev.js - a simplified SW that only handles image caching
2. Updated registration to use sw-dev.js in dev mode, sw.js in production
3. Dev SW uses simple cache-first strategy for images
This allows testing image caching in development without needing a build.
