Adds account management and subscription features

Introduces new account pages for managing subscriptions, payment methods, and invoice history

Includes:
- Subscription plan selection view
- Payment method display component
- Invoice history table
- Account page layout and styling

Updates main layout to include new CSS files for account management

PlanTempus.Application/Features/Menu/Services/MockMenuService.cs

@@ -176,7 +176,7 @@ public class MockMenuService : IMenuService
                         Id = "account",
                         Label = "Abonnement & Konto",
                         Icon = "ph-credit-card",
-                        Url = "/poc-konto.html",
+                        Url = "/konto",
                         MinimumRole = UserRole.Admin,
                         SortOrder = 2
                     }