Add SEO metadata, sitemap, robots, and JSON-LD for search ranking.

Ship canonical/Open Graph/Twitter tags, WebApplication schema, and landing copy aimed at audio-to-YouTube queries.

app/robots.ts

@@ -0,0 +1,11 @@
+import type { MetadataRoute } from "next";
+
+export default function robots(): MetadataRoute.Robots {
+  return {
+    rules: {
+      userAgent: "*",
+      allow: "/",
+    },
+    sitemap: "https://songs2vid.com/sitemap.xml",
+  };
+}