feat: update Navbar structure and enhance layout with main tag; improve robots.txt for better crawling control

frontend/src/lib/common/framework/ui/Navbar.svelte

@@ -3,7 +3,7 @@
 	import NavbarAction from '$lib/common/framework/ui/NavbarAction.svelte';
 </script>
 
-<div class="border-b border-gray-300">
+<nav class="border-b border-gray-300">
 	<div
 		class="mx-auto flex h-toolbar-height max-w-screen-xl flex-row items-center justify-between px-4 md:px-6"
 	>
@@ -20,4 +20,4 @@
 			/>
 		</div>
 	</div>
-</div>
+</nav>

frontend/src/routes/+layout.svelte

@@ -12,6 +12,8 @@
 </svelte:head>
 <div class="min-h-screen">
 	<Navbar />
+	<main>
 		<slot />
+	</main>
 </div>
 <Footer />

frontend/static/robots.txt

@@ -1,2 +1,4 @@
 User-agent: *
 Allow: /
+Disallow: /dashboard/
+Disallow: /api/