SW is now generated by next.config.ts on every build with a versioned
cache name (timestamp in prod, "dev" in dev). Strategies: stale-while-
revalidate for static chunks and navigation, network-first with 2s
timeout for API GETs, network-only for mutations. Offline mutations
postMessage to clients; pwa-register.tsx shows amber offline banner,
red mutation-failed toast, and indigo "new version" refresh prompt.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
