Add Open Graph and Twitter Card metadata for social sharing

- Add og-image.jpg (1200x630) for link previews
- Add metadataBase, openGraph, and twitter metadata to layout.tsx

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/layout.tsx

@@ -9,6 +9,7 @@ const _geistMono = Geist_Mono({ subsets: ["latin"] })
 const _permanentMarker = Permanent_Marker({ weight: "400", subsets: ["latin"] })
 
 export const metadata: Metadata = {
+  metadataBase: new URL("https://cryptocommonsgather.ing"),
   title: "Crypto Commons Gathering 2026 | CCG",
   description:
     "The sixth annual hack-ademic confluence of commons praxis and the latest cryptographic technologies in the Austrian Alps. August 16-22, 2026.",
@@ -20,6 +21,30 @@ export const metadata: Metadata = {
       },
     ],
   },
+  openGraph: {
+    title: "Crypto Commons Gathering 2026 | CCG",
+    description:
+      "The sixth annual hack-ademic confluence of commons praxis and the latest cryptographic technologies in the Austrian Alps. August 16-22, 2026.",
+    url: "https://cryptocommonsgather.ing",
+    siteName: "Crypto Commons Gathering",
+    images: [
+      {
+        url: "/og-image.jpg",
+        width: 1200,
+        height: 630,
+        alt: "Crypto Commons Gathering 2026 - Austrian Alps",
+      },
+    ],
+    locale: "en_US",
+    type: "website",
+  },
+  twitter: {
+    card: "summary_large_image",
+    title: "Crypto Commons Gathering 2026 | CCG",
+    description:
+      "The sixth annual hack-ademic confluence of commons praxis and the latest cryptographic technologies in the Austrian Alps. August 16-22, 2026.",
+    images: ["/og-image.jpg"],
+  },
 }
 
 export default function RootLayout({