feat(notification): add admin rest management and deletion

Add revision-safe service and template APIs, channel mapping, and validated admin controls.

Ref: IT-1601

HrynCo.NotificationService.Web/Views/Shared/_Layout.cshtml

@@ -16,10 +16,11 @@
     <link href="/css/admin.css" rel="stylesheet" />
 </head>
 <body>
-    <nav class="navbar navbar-dark bg-dark px-3 admin-navbar">
+    <nav class="navbar navbar-dark bg-dark admin-navbar">
         <a class="navbar-brand fw-bold" href="/">
             <i class="bi bi-bell-fill me-1"></i> Notification Service
         </a>
+        <a class="admin-api-documentation" href="/scalar/v1" target="_blank" rel="noopener noreferrer" aria-label="API documentation (opens in a new tab)">API documentation</a>
     </nav>
 
     <div class="container-fluid">
@@ -43,6 +44,7 @@
     </div>
 
     <script src="/lib/bootstrap/bootstrap.bundle.min.js"></script>
+    <script src="~/js/admin-tables.js" asp-append-version="true"></script>
     @RenderSection("Scripts", required: false)
 </body>
 </html>