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/sw.js

@@ -0,0 +1,15 @@
+// Minimal service worker for PWA installability.
+// This app requires a live WebSocket connection, so offline caching is not useful.
+// All fetch requests are passed through to the network.
+
+self.addEventListener('install', () => {
+    self.skipWaiting();
+});
+
+self.addEventListener('activate', (event) => {
+    event.waitUntil(self.clients.claim());
+});
+
+self.addEventListener('fetch', (event) => {
+    event.respondWith(fetch(event.request));
+});