Switch layout to use runes syntax

src/routes/+layout.svelte

@@ -1,10 +1,15 @@
+<svelte:options runes={true} />
+
 <script>
     import "../app.pcss";
+
+    let { children } = $props();
 </script>
 
 <div class="h-full flex flex-col">
     <div class="border border-2 p-1">
         <h1>Navbar</h1>
     </div>
-    <slot></slot>
+
+    {@render children()}
 </div>