feat: open graph + robots metadata for social sharing

Adds metadataBase, og:title/description/url/siteName/type, twitter card,
and robots index/follow to the root layout for proper link previews when
0pt.app links are shared in Slack, email, or social.

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

app/layout.tsx

@@ -15,6 +15,24 @@ export const metadata: Metadata = {
   description:
     "Data services on demand for the Nordics & Europe. Provenance per field, GDPR-native. Compose your data job, pay 50% to start, watch production live, and validate the result with full transparency.",
   generator: "0pt.app",
+  metadataBase: new URL("https://0pt.app"),
+  openGraph: {
+    title: "0pt — your data",
+    description: "Nordic & European data services. Provenance per field. GDPR-native. 50/50 escrow.",
+    url: "https://0pt.app",
+    siteName: "0pt",
+    locale: "en_US",
+    type: "website",
+  },
+  twitter: {
+    card: "summary",
+    title: "0pt — your data",
+    description: "Nordic & European data services. Provenance per field. GDPR-native.",
+  },
+  robots: {
+    index: true,
+    follow: true,
+  },
 };
 
 export default function RootLayout({ children }: Readonly<{ children: React.ReactNode }>) {