Add site metadata and serve favicon from public/

Moving favicon.ico out of app/ bypasses Next's metadata image loader,
which fails to read the .ico in sandboxed runtimes.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

app/layout.tsx

@@ -1,9 +1,40 @@
 import type { Metadata } from "next";
 import "./globals.css";
 
+const siteName = "Next.js Template";
+const siteDescription =
+  "A Next.js 16 starter with Tailwind CSS and shadcn/ui, ready to deploy on Vercel.";
+
+// Absolute origin behind `metadataBase`, so Open Graph images resolve to full
+// URLs. Vercel injects VERCEL_PROJECT_PRODUCTION_URL on deployed builds.
+const siteUrl =
+  process.env.NEXT_PUBLIC_SITE_URL ??
+  (process.env.VERCEL_PROJECT_PRODUCTION_URL
+    ? `https://${process.env.VERCEL_PROJECT_PRODUCTION_URL}`
+    : "http://localhost:3000");
+
+// Routes only set their own `title`; the template appends the site name.
 export const metadata: Metadata = {
-  title: "Create Next App",
-  description: "Generated by create next app",
+  metadataBase: new URL(siteUrl),
+  title: {
+    default: siteName,
+    template: `%s — ${siteName}`,
+  },
+  description: siteDescription,
+  // Served from public/ so it bypasses the metadata image loader.
+  icons: { icon: "/favicon.ico" },
+  openGraph: {
+    type: "website",
+    siteName,
+    title: siteName,
+    description: siteDescription,
+    url: "/",
+  },
+  twitter: {
+    card: "summary_large_image",
+    title: siteName,
+    description: siteDescription,
+  },
 };
 
 export default function RootLayout({