feat(templates): add service language template management

Add normalized service and template catalogs, scoped administration, migration, validation, and regression coverage.

Ref: IT-1601

HrynCo.NotificationService.Web/Controllers/Admin/ViewModels/EmailTemplateEditViewModel.cs

@@ -2,32 +2,20 @@ using System.ComponentModel.DataAnnotations;
 
 namespace HrynCo.NotificationService.Web.Controllers.Admin.ViewModels;
 
-public class EmailTemplateEditViewModel
+public sealed class EmailTemplateEditViewModel
 {
     public Guid? Id { get; set; }
-
-    [Required]
+    public Guid ServiceId { get; set; }
+    public Guid Revision { get; set; }
+    [Required, StringLength(100)]
     public string ServiceName { get; set; } = "";
-
-    [Required]
+    [Required, StringLength(100)]
     public string Key { get; set; } = "";
-
     [Required]
-    public string LanguageCode { get; set; } = "";
-
-    [Required]
-    public string Subject { get; set; } = "";
-
-    [Required]
-    public string HtmlBody { get; set; } = "";
-
-    public string TextBody { get; set; } = "";
-
-    // JSON array: [{"name":"UserName","required":true}, ...]
     public string VariablesJson { get; set; } = "[]";
-    public string? ServiceNameFilter { get; set; }
+    public List<EmailTemplateLanguageEditViewModel> Languages { get; set; } = [];
+    public int ActiveLanguageIndex { get; set; }
     public string? KeyFilter { get; set; }
-
     public bool IsNew => Id == null;
     public string PageTitle => IsNew ? "Create Email Template" : "Edit Email Template";
 }