refactor: channel holds delivery config only — remove AppDisplayName, AppBaseUrl

- SmtpChannelSettings: Host, Port, Username, Password, UseSsl, FromEmail, FromName only
- AppDisplayName and AppBaseUrl moved to template variables (payload responsibility)
- Updated ViewModel, controller Save/Edit mapping, and Edit view accordingly

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.Web/Controllers/Admin/AdminChannelsController.cs

@@ -55,8 +55,7 @@ public class AdminChannelsController : Controller
         var channel = result.Result;
         var smtp = channel.Settings as SmtpChannelSettings ?? new SmtpChannelSettings
         {
-            Host = "", Username = "", Password = "",
-            FromEmail = "", FromName = "", AppDisplayName = "", AppBaseUrl = ""
+            Host = "", Username = "", Password = "", FromEmail = "", FromName = ""
         };
 
         var vm = new EmailChannelEditViewModel
@@ -75,9 +74,7 @@ public class AdminChannelsController : Controller
             Password = smtp.Password,
             UseSsl = smtp.UseSsl,
             FromEmail = smtp.FromEmail,
-            FromName = smtp.FromName,
-            AppDisplayName = smtp.AppDisplayName,
-            AppBaseUrl = smtp.AppBaseUrl
+            FromName = smtp.FromName
         };
 
         return View(vm);
@@ -99,9 +96,7 @@ public class AdminChannelsController : Controller
             Password = model.Password,
             UseSsl = model.UseSsl,
             FromEmail = model.FromEmail,
-            FromName = model.FromName,
-            AppDisplayName = model.AppDisplayName,
-            AppBaseUrl = model.AppBaseUrl
+            FromName = model.FromName
         };
 
         if (model.IsNew)