Add Debug.Assert for missing OverlayDialogHost with setup guidance (#863)

* Initial plan

* Add Debug.Assert when OverlayDialogHost is not found with helpful setup instructions

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* fix: improve debug assertion message for OverlayDialogHost setup instructions

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>
Co-authored-by: Dong Bin <popmessiah@hotmail.com>

Author: Copilot

src/Ursa/Controls/OverlayShared/OverlayDialogManager.cs

@@ -23,7 +23,15 @@ public static void UnregisterHost(string? id, int? hash)
     public static OverlayDialogHost? GetHost(string? id, int? hash)
     {
         HostKey? key = hash is null ? Hosts.Keys.Where(k => k.Id == id).ToArray().FirstOrDefault() : Hosts.Keys.FirstOrDefault(k => k.Id == id && k.Hash == hash);
-        if (key is null) return null;
+        if (key is null)
+        {
+            Debug.Assert(false, 
+                "OverlayDialogHost not found. Please ensure the host is properly set up with one of below method:\n" +
+                "1. Use UrsaWindow or UrsaView which includes a default OverlayDialogHost in their control templates, or\n" +
+                "2. Add an OverlayDialogHost control with a HostId property to your view.\n" +
+                "For more information, see: https://docs.irihi.tech/ursa/docs/advanced/dialog-and-drawer/overlay-dialoghost");
+            return null;
+        }
         return Hosts.TryGetValue(key.Value, out var host) ? host : null;
     }
 }