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/Views/AdminServices/Index.cshtml

@@ -0,0 +1,14 @@
+@using HrynCo.NotificationService.DAL.Abstract.Templates
+@model IReadOnlyList<NotificationServiceInfo>
+@{ ViewData["Title"] = "Services"; }
+<div class="page-header"><h2>Services</h2><a href="/admin/services/create" class="btn btn-primary">Create service</a></div>
+@if (Model.Count == 0) { <p>No services yet. Create a service and its language codes before adding templates.</p> }
+else
+{
+    <div class="table-responsive"><table class="table table-hover"><thead><tr><th>Name</th><th>Language codes</th><th class="service-actions">Action</th></tr></thead><tbody>
+    @foreach (var service in Model)
+    {
+        <tr><td><a href="/admin/services/@service.Id">@service.Name</a></td><td>@string.Join(", ", service.Languages.Select(l => l.Code))</td><td class="service-actions"><a href="/admin/services/@service.Id/edit" class="btn btn-outline-primary btn-sm" aria-label="Edit service @service.Name">Edit</a></td></tr>
+    }
+    </tbody></table></div>
+}