chore: rebrand zu Dockly-Pfandsystem

Anzeige-Name ueberall umgestellt:
- index.html title, Login-H1, TopNav, SuperAdmin-Header
- Mail-Subject, HTML-Body, Default-MAIL_FROM
- PWA Manifest name (short_name: Dockly-Pfand wegen Laengen-Limit)

src/components/SuperAdmin.jsx

@@ -27,7 +27,7 @@ export default function SuperAdmin({ user, onLogout }) {
         <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.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>
+            <span className="font-semibold">Dockly-Pfandsystem · SuperAdmin</span>
           </div>
           <div className="text-sm text-slate-500 mr-3 hidden sm:block">{user.email}</div>
           <button onClick={onLogout} className="btn-ghost"><FaSignOutAlt /> Abmelden</button>