Make guidebook remember where you left off (#31375)

* Guidebook tracks last read entry

* Persistent guidebook fixes

* Persistent guidebook requested changes

* Update Content.Client/UserInterface/Systems/Guidebook/GuidebookUIController.cs

---------

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>

Content.Client/Guidebook/Controls/GuidebookWindow.xaml.cs

@@ -23,6 +23,8 @@ public sealed partial class GuidebookWindow : FancyWindow, ILinkClickHandler
 
     private readonly ISawmill _sawmill;
 
+    public ProtoId<GuideEntryPrototype> LastEntry;
+
     public GuidebookWindow()
     {
         RobustXamlLoader.Load(this);
@@ -90,6 +92,8 @@ public sealed partial class GuidebookWindow : FancyWindow, ILinkClickHandler
 
             _sawmill.Error($"Failed to parse contents of guide document {entry.Id}.");
         }
+
+        LastEntry = entry.Id;
     }
 
     public void UpdateGuides(