feat: Implement Authentik group synchronization and add confirmation dialogs for service management

OTSSignsOrchestrator.Core/Models/DTOs/AuthentikGroupItem.cs

@@ -0,0 +1,18 @@
+namespace OTSSignsOrchestrator.Core.Models.DTOs;
+
+/// <summary>
+/// Represents an Authentik group for display and sync operations.
+/// </summary>
+public class AuthentikGroupItem
+{
+    public string Pk { get; set; } = string.Empty;
+    public string Name { get; set; } = string.Empty;
+    public int MemberCount { get; set; }
+
+    /// <summary>Display text for UI: "Group Name (N members)".</summary>
+    public string DisplayText => MemberCount > 0
+        ? $"{Name}  ({MemberCount} member{(MemberCount == 1 ? "" : "s")})"
+        : Name;
+
+    public override string ToString() => DisplayText;
+}