feat: improve accessibility and SEO (100/100 Lighthouse score)

Fixes color contrast, canonical URLs, viewport scaling, semantic lists,

and resolves 404 errors for manifest/imgproxy.

app/[locale]/layout.tsx

@@ -24,29 +24,37 @@ const inter = Inter({
   variable: '--font-inter',
 });
 
-export const metadata: Metadata = {
-  metadataBase: new URL(SITE_URL),
-  alternates: {
-    canonical: '/',
-    languages: {
-      de: '/de',
-      en: '/en',
+export async function generateMetadata(props: {
+  params: Promise<{ locale: string }>;
+}): Promise<Metadata> {
+  const params = await props.params;
+  const { locale } = params;
+
+  return {
+    metadataBase: new URL(SITE_URL),
+    manifest: '/manifest.webmanifest',
+    alternates: {
+      canonical: locale === 'en' ? '/' : `/${locale}`,
+      languages: {
+        de: '/de',
+        en: '/en',
+      },
     },
-  },
-  icons: {
-    icon: [
-      { url: '/favicon.ico', sizes: 'any' },
-      { url: '/logo-blue.svg', type: 'image/svg+xml' },
-    ],
-    apple: [{ url: '/apple-touch-icon.png', sizes: '180x180', type: 'image/png' }],
-  },
-};
+    icons: {
+      icon: [
+        { url: '/favicon.ico', sizes: 'any' },
+        { url: '/logo-blue.svg', type: 'image/svg+xml' },
+      ],
+      apple: [{ url: '/apple-touch-icon.png', sizes: '180x180', type: 'image/png' }],
+    },
+  };
+}
 
 export const viewport: Viewport = {
   width: 'device-width',
   initialScale: 1,
-  maximumScale: 1,
-  userScalable: false,
+  maximumScale: 5,
+  userScalable: true,
   viewportFit: 'cover',
   themeColor: '#001a4d',
 };