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.Services/EmailTemplates/GetAll/GetAllEmailTemplatesHandler.cs

@@ -0,0 +1,30 @@
+using HrynCo.NotificationService.DAL.Abstract;
+using HrynCo.NotificationService.DAL.Abstract.Repositories;
+using HrynCo.NotificationService.DAL.Abstract.Templates;
+using HrynCo.NotificationService.Services.Core;
+using HrynCo.NotificationService.Services.Logging;
+using static HrynCo.NotificationService.Services.Core.ServiceResultHelper;
+
+namespace HrynCo.NotificationService.Services.EmailTemplates.GetAll;
+
+internal sealed class GetAllEmailTemplatesHandler
+    : RequestHandler<GetAllEmailTemplatesQuery, ServiceResult<IReadOnlyList<EmailTemplate>>>
+{
+    private readonly IEmailTemplateRepository _templates;
+
+    public GetAllEmailTemplatesHandler(
+        IContextualSerilogLogger<GetAllEmailTemplatesQuery> logger,
+        IUnitOfWork unitOfWork,
+        IEmailTemplateRepository templates)
+        : base(logger, unitOfWork)
+    {
+        _templates = templates;
+    }
+
+    protected override async Task<ServiceResult<IReadOnlyList<EmailTemplate>>> DoOnHandle(
+        GetAllEmailTemplatesQuery request, CancellationToken cancellationToken)
+    {
+        var templates = await _templates.GetAllAsync(cancellationToken);
+        return Success(templates);
+    }
+}