Share previews: Open Graph and Twitter tags, a share card and a touch icon

The tags live in app.html because link scrapers do not run the client,
and the card and icon are rendered from the site's own palette and the
Spellcast snap silhouette.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/routes/+page.svelte

@@ -40,7 +40,6 @@
 
 <svelte:head>
 	<title>Waving Hands</title>
-	<meta name="description" content="A duel of gestures against a rival wizard, after Richard Bartle's 1977 pencil-and-paper game." />
 </svelte:head>
 
 <header class="masthead">