Add _routes.json configuration to properly handle direct /r/ and /a/ paths
on Cloudflare Pages deployments. This ensures that client-side routes are
served correctly instead of returning 404 errors.
- Implement Service Worker to intercept and cache image requests
- Service Worker persists across hard reloads unlike Cache API alone
- Simplify useImageCache hook to work with Service Worker
- Images now work offline even after hard reload
- Service Worker handles transparent cache-first serving for images
- Add _headers for security headers and asset caching
- Add robots.txt for SEO with sitemap reference
- Add _redirects for SPA client-side routing support
