feat: comprehensive SEO — meta tags, OG, Twitter cards, JSON-LD, sitemap, robots, llms.txt

Adds metadataBase, full OpenGraph + Twitter card tags, keywords,
JSON-LD structured data (SoftwareApplication + Organization),
sitemap.ts, robots.ts with AI crawler directives, and llms.txt
for AI agent discoverability.

apps/web/src/app/sitemap.ts

@@ -0,0 +1,9 @@
+import { MetadataRoute } from "next";
+
+export default function sitemap(): MetadataRoute.Sitemap {
+  const baseUrl = "https://agentlens.vectry.tech";
+  return [
+    { url: baseUrl, lastModified: new Date(), changeFrequency: "weekly", priority: 1.0 },
+    { url: `${baseUrl}/dashboard`, lastModified: new Date(), changeFrequency: "daily", priority: 0.8 },
+  ];
+}