enhance-pwa — Make It Installable and Offline-Ready

A PWA closes the gap between "website" and "app". Users can install it to their home screen, it loads instantly from cache, and it keeps working when the network drops. This skill adds those capabilities to any existing web app without breaking what already works.

Phase 0: Audit what already exists

public/manifest.json or public/manifest.webmanifest  → existing manifest
public/sw.js or src/sw.ts                             → existing service worker
vite.config.*   → vite-plugin-pwa already configured?
next.config.*   → next-pwa already configured?
package.json    → workbox-*, vite-plugin-pwa, next-pwa, @vite-pwa/nuxt