style: pfandlogo.png statt .jpg (transparente Version)

- public/pfandlogo.png ersetzt pfandlogo.jpg
- Alle Referenzen umgestellt (Login, TopNav, SuperAdmin, index.html, manifest.json)
- favicon type=image/png

public/manifest.json

@@ -7,7 +7,7 @@
   "theme_color": "#051e23",
   "description": "Digitale Pfand- und Tourenverwaltung",
   "icons": [
-    { "src": "pfandlogo.jpg", "sizes": "1000x1000", "type": "image/jpeg" },
+    { "src": "pfandlogo.png", "sizes": "1000x1000", "type": "image/png" },
     { "src": "icon-192.png", "sizes": "192x192", "type": "image/png" },
     { "src": "icon-512.png", "sizes": "512x512", "type": "image/png" }
   ]