refactor: Add analytics script to layout for tracking website usage

frontend/src/routes/+layout.svelte

@@ -3,8 +3,17 @@
 	import Toast from '$lib/components/Toast.svelte';
 	import 'tailwindcss/tailwind.css';
 	export let data;
+
+	const enableAnalytics = process.env['ENABLE_ANALYTICS'] || 'false';
+	const unamiKey = process.env['UNAMI_KEY'] || '';
 </script>
 
+<svelte:head>
+	{#if enableAnalytics === 'true' && unamiKey}
+		<script defer src="https://cloud.umami.is/script.js" data-website-id={unamiKey}></script>
+	{/if}
+</svelte:head>
+
 <Navbar {data} />
 <Toast />