feat: add OG image and Twitter Card meta tags for link previews

The og-image.png was referenced in meta tags but never created. Generate
a 1200x630 parchment-themed OG image and add missing twitter:title,
twitter:description, and twitter:image meta tags for proper social
media link previews.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

website/index.html

@@ -11,6 +11,9 @@
 	<meta property="og:url" content="https://crumbs.bretzel.app">
 	<meta property="og:image" content="https://crumbs.bretzel.app/assets/og-image.png">
 	<meta name="twitter:card" content="summary_large_image">
+	<meta name="twitter:title" content="Crumbs by Bretzel">
+	<meta name="twitter:description" content="Self-hostable, offline-first note-taking. A Google Keep alternative that respects your privacy.">
+	<meta name="twitter:image" content="https://crumbs.bretzel.app/assets/og-image.png">
 	<link rel="icon" type="image/png" sizes="96x96" href="assets/favicon-96x96.png">
 	<link rel="icon" type="image/x-icon" href="assets/favicon.ico">
 	<script defer src="https://umami.bretzel.app/script.js" data-website-id="5969ad34-0b49-4af4-bddf-b026358a97af"></script>