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.DAL.EF/Repositories/EmailTemplateRepository.cs

@@ -12,6 +12,12 @@ internal sealed class EmailTemplateRepository : EfRepository<EmailTemplateEntity
     {
     }
 
+    public async Task<IReadOnlyList<EmailTemplate>> GetAllAsync(CancellationToken ct = default)
+    {
+        List<EmailTemplateEntity> entities = await DbSet.ToListAsync(ct);
+        return entities.Select(MapToDomain).ToList();
+    }
+
     public async Task<IReadOnlyList<EmailTemplate>> GetByServiceAsync(string serviceName, CancellationToken ct = default)
     {
         List<EmailTemplateEntity> entities = await DbSet