Restructures project with feature-based organization

Refactors project structure to support modular, feature-driven development

Introduces comprehensive language localization support
Adds menu management with role-based access control
Implements dynamic sidebar and theme switching capabilities

Enhances project scalability and maintainability

app/Features/Menu/Models/UserRole.cs

@@ -0,0 +1,11 @@
+namespace CalendarServer.Features.Menu.Models;
+
+/// <summary>
+/// User roles for menu visibility. Higher value = more access.
+/// </summary>
+public enum UserRole
+{
+    Staff = 0,
+    Manager = 1,
+    Admin = 2
+}