GuestLog - User message improvements

- Added UserMessageService to have common methods for showing messages and errors to the user.
- Added Result record so services can return status on operation error (so it can be shown in the UI messages).
- Updated services to use the new Result record.
- Updated pages to use the new IUserMessageService.

src/Somnia.GuestLog/Components/Pages/StayEntries/StayEntryDetail.razor

@@ -3,7 +3,7 @@
 @using Somnia.GuestLog.Models.DTOs;
 @using Somnia.GuestLog.Services;
 
-@inject ISnackbar Snackbar
+@inject IUserMessageService userMessage
 @inject IDialogService DialogService
 @inject NavigationManager Navigation
 @inject IGuestDocumentService guestDocService
@@ -54,7 +54,7 @@
         stayModel = await stayService.GetDtoByIdAsync(StayId, queryConfig: new(IncludeGuests: true));
         if (stayModel is null)
         {
-            Snackbar.Add($"Stay not found with ID: '{StayId}'", Severity.Error);
+            userMessage.ShowMessage($"Stay not found with ID: '{StayId}'", MessageKind.Error);
             Navigation.NotFound();
             return;
         }
@@ -62,7 +62,7 @@
 
     private void BtnEdit()
     {
-        Snackbar.Add("Not implemented yet!", Severity.Info);
+        userMessage.ShowMessage("Not implemented yet!", MessageKind.Info);
     }
 
     private void BtnReturn()