Add DevBanner

src/routes/+layout.svelte

@@ -1,5 +1,7 @@
 <script>
   import '../app.css';
+  import { dev } from '$app/environment';
+  import DevBanner from '$lib/DevBanner.svelte';
 </script>
 
 <svelte:head>
@@ -14,4 +16,7 @@
   <link rel="manifest" href="/manifest.json" />
   <title>OwlBoard</title>
 </svelte:head>
+{#if dev}
+    <DevBanner />
+{/if}
 <slot />