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)

public/manifest.json

@@ -1,6 +1,6 @@
 {
-  "name": "Pfandsystem",
-  "short_name": "Pfandsystem",
+  "name": "Dockly-Pfandsystem",
+  "short_name": "Dockly-Pfand",
   "start_url": ".",
   "display": "standalone",
   "background_color": "#f8fafc",