Adds Online group to application menu and localization

Introduces new menu group with Booking and Website sections
Updates Danish localization to include new menu items and group

Enhances application navigation with online-related features

PlanTempus.Application/Features/Localization/Translations/da.json

@@ -8,6 +8,8 @@
     "customers": "Kunder",
     "employees": "Medarbejdere",
     "services": "Services",
+    "booking": "Booking",
+    "website": "Website",
     "reports": "Statistik & Rapporter",
     "settings": "Indstillinger",
     "account": "Abonnement & Konto"
@@ -15,6 +17,7 @@
   "groups": {
     "overview": "Overblik",
     "data": "Data",
+    "online": "Online",
     "analytics": "Analyse",
     "system": "System"
   },