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

src/components/SuperAdmin.jsx

@@ -26,7 +26,7 @@ export default function SuperAdmin({ user, onLogout }) {
       <header className="bg-white border-b border-slate-200 sticky top-0 z-30">
         <div className="max-w-6xl mx-auto px-4 sm:px-6 h-14 flex items-center">
           <div className="flex items-center gap-2 flex-1">
-            <img src="/pfandlogo.jpg" alt="" className="h-8 w-8 rounded-lg object-contain bg-white ring-1 ring-slate-200 p-0.5" />
+            <img src="/pfandlogo.png" alt="" className="h-8 w-8 rounded-lg object-contain bg-white ring-1 ring-slate-200 p-0.5" />
             <span className="font-semibold">Pfandsystem · SuperAdmin</span>
           </div>
           <div className="text-sm text-slate-500 mr-3 hidden sm:block">{user.email}</div>