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/src/domain/umami-payload.ts

@@ -0,0 +1,35 @@
+/**
+ * Maps page view facts onto the Umami /api/send contract.
+ * A page view is an unnamed event: no `name`, no `data`.
+ * The client identity (user agent, IP) travels as request headers, not in
+ * the payload — see src/analytics/recordPageviewToUmami.ts.
+ */
+
+import type { PageviewFacts } from "./pageview-decision";
+
+export type UmamiSendBody = {
+  readonly type: "event";
+  readonly payload: {
+    readonly website: string;
+    readonly hostname: string;
+    readonly language: string;
+    readonly referrer: string;
+    readonly url: string;
+  };
+};
+
+export function buildUmamiPageviewBody(
+  facts: PageviewFacts,
+  websiteId: string,
+): UmamiSendBody {
+  return {
+    type: "event",
+    payload: {
+      website: websiteId,
+      hostname: facts.hostname,
+      language: facts.language,
+      referrer: facts.referrer,
+      url: facts.url,
+    },
+  };
+}