Add GetCities function to ServersRepository class.

ServerManagement/Models/ServersRepository.cs

@@ -76,5 +76,15 @@ namespace ServerManagement.Models
         {
             return servers.Where(s => s.Name.Contains(serverFilter, StringComparison.OrdinalIgnoreCase)).ToList();
         }
+
+        public static List<string> GetCities()
+        {
+            return servers
+            .Select(s => s.City)
+            .Where(city => !string.IsNullOrEmpty(city))
+            .Select(city => city!) // Null-forgiving operator
+            .Distinct()
+            .ToList();
+        }
     }
 }