feat(Layout): add font loading flag and change head links to prevent FOUT

src/app/ui/Layout.svelte

@@ -15,32 +15,69 @@ import GD from '$shared/assets/GD.svg';
 import { ResponsiveProvider } from '$shared/lib';
 import { ScrollArea } from '$shared/shadcn/ui/scroll-area';
 import { Provider as TooltipProvider } from '$shared/shadcn/ui/tooltip';
-import type { Snippet } from 'svelte';
+import {
+    type Snippet,
+    onMount,
+} from 'svelte';
 
 interface Props {
     children: Snippet;
 }
 
-/** Slot content for route pages to render */
 let { children }: Props = $props();
+let fontsReady = $state(false);
+
+/**
+ * Sets fontsReady flag to true when font for the page logo is loaded.
+ */
+onMount(async () => {
+    if (!('fonts' in document)) {
+        fontsReady = true;
+        return;
+    }
+
+    const required = ['100'];
+
+    const missing = required.filter(
+        w => !document.fonts.check(`${w} 1em Barlow`),
+    );
+
+    if (missing.length > 0) {
+        await Promise.all(
+            missing.map(w => document.fonts.load(`${w} 1em Barlow`)),
+        );
+    }
+    fontsReady = true;
+});
+
+$inspect(fontsReady);
 </script>
 
 <svelte:head>
     <link rel="icon" href={GD} />
+
     <link rel="preconnect" href="https://api.fontshare.com" />
     <link rel="preconnect" href="https://cdn.fontshare.com" crossorigin="anonymous" />
 
     <link rel="preconnect" href="https://fonts.googleapis.com">
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin="anonymous">
     <link
-        href="https://fonts.googleapis.com/css2?family=Karla:ital,wght@0,200..800;1,200..800&display=swap"
-        rel="stylesheet"
+        rel="preload"
+        as="style"
+        href="https://fonts.googleapis.com/css2?family=Barlow:ital,wght@0,100;0,200;1,100;1,200&family=Karla:wght@200..800&display=swap"
     >
     <link
-        href="https://fonts.googleapis.com/css2?family=Barlow:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,100;1,200;1,300;1,400;1,500;1,600;1,700;1,800;1,900&family=Karla:wght@300&display=swap"
         rel="stylesheet"
+        href="https://fonts.googleapis.com/css2?family=Barlow:ital,wght@0,100;0,200;1,100;1,200&family=Karla:wght@200..800&display=swap"
+        media="print"
+        onload={(e => ((e.currentTarget as HTMLLinkElement).media = 'all'))}
     >
-
+    <noscript>
+        <link
+            rel="stylesheet"
+            href="https://fonts.googleapis.com/css2?family=Barlow:ital,wght@0,100;0,200;1,100;1,200&family=Karla:wght@200..800&display=swap"
+        >
+    </noscript>
     <title>
         Compare Typography & Typefaces | GlyphDiff
     </title>
@@ -55,7 +92,9 @@ let { children }: Props = $props();
         <!-- <ScrollArea class="h-screen w-screen"> -->
         <main class="flex-1 h-full w-full max-w-6xl mx-auto px-0 pt-0 pb-10 sm:px-6 sm:pt-8 sm:pb-12 md:px-8 md:pt-10 md:pb-16 lg:px-10 lg:pt-12 lg:pb-20 xl:px-16 relative overflow-x-hidden">
             <TooltipProvider>
+                {#if fontsReady}
                     {@render children?.()}
+                {/if}
             </TooltipProvider>
         </main>
         <!-- </ScrollArea> -->