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/Shared/_Layout.cshtml

@@ -1,6 +1,7 @@
 @{
     var currentController = ViewContext.RouteData.Values["controller"]?.ToString() ?? "";
-    bool isTemplates = currentController.Equals("AdminTemplates", StringComparison.OrdinalIgnoreCase);
+    bool isServices = currentController.Equals("AdminServices", StringComparison.OrdinalIgnoreCase)
+        || currentController.Equals("AdminTemplates", StringComparison.OrdinalIgnoreCase);
     bool isChannels  = currentController.Equals("AdminChannels",  StringComparison.OrdinalIgnoreCase);
 }
 <!DOCTYPE html>
@@ -26,11 +27,7 @@
             <nav class="col-md-2 d-none d-md-block sidebar py-3">
                 <div class="sidebar-section-label">Management</div>
                 <ul class="nav flex-column px-2">
-                    <li class="nav-item">
-                        <a class="nav-link @(isTemplates ? "active" : "")" href="/admin/templates">
-                            <i class="bi bi-envelope-paper"></i> Email Templates
-                        </a>
-                    </li>
+                    <li class="nav-item"><a class="nav-link @(isServices ? "active" : "")" href="/admin/services"><i class="bi bi-collection"></i> Services</a></li>
                     <li class="nav-item">
                         <a class="nav-link @(isChannels ? "active" : "")" href="/admin/channels">
                             <i class="bi bi-broadcast"></i> Email Channels