NPC refactor (#10122)

Co-authored-by: metalgearsloth <metalgearsloth@gmail.com>

Content.Client/NPC/NPCEui.cs

@@ -0,0 +1,22 @@
+using Content.Client.Eui;
+
+namespace Content.Client.NPC;
+
+public sealed class NPCEui : BaseEui
+{
+    private NPCWindow? _window = new();
+
+    public override void Opened()
+    {
+        base.Opened();
+        _window = new NPCWindow();
+        _window.OpenCentered();
+    }
+
+    public override void Closed()
+    {
+        base.Closed();
+        _window?.Close();
+        _window = null;
+    }
+}