feat: add MVC Razor admin UI for email templates

- GetAllEmailTemplatesQuery + handler (new GetAll use case)
- IEmailTemplateRepository.GetAllAsync + EF implementation
- AdminTemplatesController: Index, Create, Edit, Save, Delete
- EmailTemplateEditViewModel with IsNew/PageTitle helpers
- Views/_ViewStart, _ViewImports, Shared/_Layout (Bootstrap 5)
- Shared/_EditorLayout (chained layout for all edit screens)
- Views/AdminTemplates/Index (table with edit/delete actions)
- Views/AdminTemplates/Edit (card form, readonly composite key on edit)
- Program.cs: AddControllersWithViews, UseStaticFiles, MapDefaultControllerRoute

Ref: IT-634

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

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

@@ -0,0 +1,31 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace HrynCo.NotificationService.Web.Controllers.Admin.ViewModels;
+
+public class EmailTemplateEditViewModel
+{
+    public Guid? Id { get; set; }
+
+    [Required]
+    public string ServiceName { get; set; } = "";
+
+    [Required]
+    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 bool IsNew => Id == null;
+    public string PageTitle => IsNew ? "Create Email Template" : "Edit Email Template";
+}