Add self-hosted Umami analytics tracker

Loads the Umami tracking script (self-hosted on Railway) from the root
layout. Cookieless; data-domains limits it to the production hostname so
local dev and forks send nothing.

Claude-Session: https://claude.ai/code/session_01Mueq43RBXxQtHRF76Rz47S

Author: gereonelvers

src/app/layout.tsx

@@ -1,4 +1,5 @@
 import type { Metadata } from "next";
+import Script from "next/script";
 import { Geist, Geist_Mono } from "next/font/google";
 import "./globals.css";
 import 'katex/dist/katex.min.css';
@@ -32,6 +33,14 @@ export default function RootLayout({
         className={`${geistSans.variable} ${geistMono.variable} antialiased`}
       >
         {children}
+        {/* Umami analytics — self-hosted on Railway, cookieless. data-domains restricts
+            tracking to the production hostname, so local dev and forks send nothing. */}
+        <Script
+          src="https://analytics-production-d4f3.up.railway.app/script.js"
+          data-website-id="3755ee1d-ade3-4a47-a70f-d799fff494bd"
+          data-domains="neural-processing-lab.github.io"
+          strategy="afterInteractive"
+        />
       </body>
     </html>
   );