feat(analytics): record pageviews server-side only

Umami never received data: the client-side path (browser beacon to
/stats/api/send) has been dead in production. Pageviews are now
classified and recorded entirely on the server in the request proxy;
no tracking script ships to the browser anymore.

- Pure domain decision (decidePageview) filters real page views from
  assets, infrastructure paths, prefetches and bot user agents
- Pure payload builder maps facts onto the Umami send contract as an
  unnamed event, with the client identity travelling in headers
- proxy.ts wires request facts into the domain and fires the send
  without delaying the response; configured via UMAMI_WEBSITE_ID and
  UMAMI_API_ENDPOINT
- Removes the dead client analytics stack (components, adapters,
  /stats proxy route) and its layout mount

apps/web/app/(site)/layout.tsx

@@ -1,6 +1,5 @@
 import type { Metadata } from "next";
 import { Inter, JetBrains_Mono, Newsreader } from "next/font/google";
-import { Analytics } from "@/src/components/Analytics";
 import { BitBurst } from "@/src/components/bits/BitBurst";
 import { Footer } from "@/src/components/Footer";
 import { Header } from "@/src/components/Header";
@@ -72,7 +71,6 @@ export default function RootLayout({
         <Footer />
         <InteractiveElements />
         <BitBurst />
-        <Analytics />
       </body>
     </html>
   );