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/manifest.json

@@ -0,0 +1,23 @@
+{
+  "name": "Media Server",
+  "short_name": "Media",
+  "description": "Remote media player control and file browser",
+  "start_url": "/",
+  "display": "standalone",
+  "orientation": "any",
+  "background_color": "#121212",
+  "theme_color": "#121212",
+  "icons": [
+    {
+      "src": "/static/icons/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml"
+    },
+    {
+      "src": "/static/icons/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "maskable"
+    }
+  ]
+}