feat(layout): add metadata base URL configuration for dynamic app URL

- Configured `metadataBase` in `RootLayout` using `NEXT_PUBLIC_APP_URL` with a fallback to the default URL.

frontend/src/app/layout.tsx

@@ -49,6 +49,9 @@ export const metadata: Metadata = {
 		images: ["/memegoat-og.png"],
 	},
 	icons: "/memegoat-color.svg",
+	metadataBase: new URL(
+		process.env.NEXT_PUBLIC_APP_URL || "https://memegoat.fr",
+	),
 };
 
 export default function RootLayout({