chore(pwa): desktop install polish for manifest

Add PNG icons (192/512) for a crisp taskbar/Start-menu icon, drop the
portrait orientation lock so the window resizes freely on desktop, and add
a stable app id. Installs as a standalone desktop window.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/manifest.json

@@ -1,18 +1,24 @@
 {
   "name": "NovaSonic",
   "short_name": "NovaSonic",
-  "description": "Self-hosted music streaming PWA",
+  "description": "Self-hosted music streaming für Navidrome / Subsonic",
+  "id": "/",
   "start_url": "/",
   "scope": "/",
   "display": "standalone",
-  "orientation": "portrait-primary",
   "background_color": "#07070f",
   "theme_color": "#07070f",
   "icons": [
     {
-      "src": "icon.svg",
-      "sizes": "any",
-      "type": "image/svg+xml",
+      "src": "icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "any"
+    },
+    {
+      "src": "icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
       "purpose": "any"
     },
     {