fix(scoring): PWA installierbar + Mikrofon auf Android/Chrome

Web-App-Manifest, Service Worker und Icons für Install-Prompt;
Permissions-Policy erlaubt Mikrofon (self); getUserMedia vor Speech API.

Co-authored-by: Cursor <cursoragent@cursor.com>

public/scoring/manifest.webmanifest

@@ -0,0 +1,32 @@
+{
+  "name": "Scoring — zwei Spieler",
+  "short_name": "Scoring",
+  "description": "Punktestand für zwei Spieler mit Spracheingabe",
+  "start_url": "./",
+  "scope": "./",
+  "display": "standalone",
+  "orientation": "any",
+  "theme_color": "#0f1117",
+  "background_color": "#0f1117",
+  "lang": "de",
+  "icons": [
+    {
+      "src": "icons/icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "any"
+    },
+    {
+      "src": "icons/icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any"
+    },
+    {
+      "src": "icons/icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    }
+  ]
+}