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)

vite.config.js

@@ -8,8 +8,8 @@ export default defineConfig({
     VitePWA({
       registerType: 'autoUpdate',
       manifest: {
-        name: 'Pfandsystem',
-        short_name: 'Pfandsystem',
+        name: 'Dockly-Pfandsystem',
+        short_name: 'Dockly-Pfand',
         start_url: '.',
         display: 'standalone',
         background_color: '#f8fafc',