Add PWA support: installable standalone app with safe area handling

- Service worker, manifest, and SVG icon for PWA installability
- Root /sw.js route for full-scope service worker registration
- Meta tags: theme-color, apple-mobile-web-app, viewport-fit=cover
- Safe area insets for notched phones (container, mini-player, footer, banner)
- Dynamic theme-color sync on light/dark toggle
- Overscroll prevention and touch-action optimization
- Hide mini-player prev/next buttons on small screens
- Updated README with PWA and new feature documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

media_server/static/js/main.js

@@ -10,6 +10,11 @@ window.addEventListener('DOMContentLoaded', async () => {
     initTheme();
     initAccentColor();
 
+    // Register service worker for PWA installability
+    if ('serviceWorker' in navigator) {
+        navigator.serviceWorker.register('/sw.js').catch(() => {});
+    }
+
     // Initialize vinyl mode
     applyVinylMode();