feat(website): SEO, a11y, and build pipeline overhaul

- SEO: per-locale og:locale, Organization+WebSite schema, FAQPage replacing ItemList
- SEO: BreadcrumbList on legal pages, site.webmanifest, expanded sitemap
- a11y: hamburger ARIA+ESC, skip-to-content, aria-hidden on step-num
- a11y: focus-visible states, prefers-reduced-motion, emoji→SVG icons
- CSS: extract .mock-section-label, replace transition:all, will-change hints
- Build: esbuild JS minifier (-46%), sharp AVIF conversion (26 files, quality 70)
- Build: content hashing (style.XXXX.min.css), SVG minification, picture injection
- Cleanup: remove lightningcss (caused CSS merging bugs)

website/datenschutz.html

@@ -9,6 +9,17 @@
     <link rel="icon" type="image/webp" href="assets/NewLogoIcon_64.webp">
     <meta name="robots" content="noindex">
 
+    <script type="application/ld+json">
+    {
+      "@context": "https://schema.org",
+      "@type": "BreadcrumbList",
+      "itemListElement": [
+        { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://sync.koalastuff.net/" },
+        { "@type": "ListItem", "position": 2, "name": "Privacy Policy", "item": "https://sync.koalastuff.net/datenschutz" }
+      ]
+    }
+    </script>
+
     <!-- Mobile Browser Theme Styling -->
     <meta name="theme-color" content="#0f172a">
     <meta name="apple-mobile-web-app-capable" content="yes">