PakStream — PWA Enablement

This update makes PakStream installable and Lighthouse‑clean for the PWA audits, with minimal and safe caching.

Added / Updated

manifest.webmanifest: proper name/short_name, / scope & start URL, theme/background colors, description, maskable icons (192/256/384/512), and screenshots (wide & mobile).
sw.js: tiny service worker with:
- CACHE_NAME = "pakstream-shell-v1" (bump this to invalidate)
- Precache a small shell (home, manifest, offline page, global CSS/JS, icons).
- Navigation: network‑first with /offline.html fallback.
- Static assets: stale‑while‑revalidate for .css, .js, images, fonts.
- Never caches media streams (.mp3, .aac, .m3u8, .mp4, etc.) or any cross‑origin requests (YouTube, radio CDNs).
- Uses self.skipWaiting() and clients.claim().
/offline.html: branded fallback page.
/js/pwa.js: registers the service worker on window.load.
HTML head & body injections across pages:
- <link rel="manifest" ...>, <meta name="theme-color" ...>, iOS meta & touch icon.
- <script src="/js/pwa.js" defer></script> before </body>.
YouTube initializer patched to add enablejsapi=1 & origin params.
Icons & Screenshots: generated clean maskable icons and mock screenshots if missing.

Edit sw.js and change:

const CACHE_NAME = "pakstream-shell-v1"; // e.g., pakstream-shell-v2

Commit & deploy; clients will update on next load.

Register/Offline
- Open DevTools → Application → Service Workers.
- Ensure the worker is activated. Check Offline in the Network panel.
- Refresh → you should see /offline.html for navigations.
Installability
- In DevTools → Application → Manifest, confirm: no errors, icons show, screenshots listed.
- Visit the site in a non‑Incognito window. Look for the Install icon in the address bar (Chrome) or use Chrome menu → Install PakStream.
Playback
- With network on, verify radio/YouTube still play normally.
- With network off, verify they do not start (by design).