feat: SEO improvements — Twitter cards, canonical URL, sitemap, robots, llms.txt

Adds metadataBase, og:image, og:url, Twitter card tags, canonical
URL, sitemap.ts, robots.ts with AI crawler directives, and llms.txt.

apps/web/src/app/layout.tsx

@@ -17,11 +17,13 @@ const jetbrainsMono = JetBrains_Mono({
 });
 
 export const metadata: Metadata = {
+  metadataBase: new URL("https://codeboard.vectry.tech"),
   title: "CodeBoard — Understand any codebase in 5 minutes",
   description:
     "Paste a GitHub URL and get interactive onboarding documentation with architecture diagrams, module breakdowns, and getting started guides. Built by Vectry AI consultancy.",
   keywords: ["code analysis", "documentation", "github", "codebase", "AI", "developer tools"],
   authors: [{ name: "Vectry" }],
+  creator: "Vectry",
   icons: {
     icon: [
       { url: "/favicon.ico", sizes: "any" },
@@ -35,6 +37,31 @@ export const metadata: Metadata = {
     description:
       "Paste a GitHub URL and get interactive onboarding documentation with architecture diagrams, module breakdowns, and getting started guides.",
     type: "website",
+    url: "https://codeboard.vectry.tech",
+    siteName: "CodeBoard",
+    locale: "en_US",
+    images: [
+      {
+        url: "/og-image.png",
+        width: 1200,
+        height: 630,
+        alt: "CodeBoard — Understand any codebase in 5 minutes",
+      },
+    ],
+  },
+  twitter: {
+    card: "summary_large_image",
+    title: "CodeBoard — Understand any codebase in 5 minutes",
+    description:
+      "Paste a GitHub URL and get interactive onboarding documentation with architecture diagrams, module breakdowns, and getting started guides.",
+    images: ["/og-image.png"],
+  },
+  alternates: {
+    canonical: "https://codeboard.vectry.tech",
+  },
+  robots: {
+    index: true,
+    follow: true,
   },
 };