fix(seed-contract-probe): send Origin header so /api/bootstrap boundary check doesn't 401 (koala73#3100)

* fix(seed-contract-probe): send Origin header so /api/bootstrap boundary check doesn't 401

Production probe returned {boundary: [{endpoint: '/api/bootstrap', pass: false,
status: 401, reason: 'status:401'}]}. Root cause: checkPublicBoundary's
self-fetch had no Origin header, so /api/bootstrap's validateApiKey() treated
it as a non-browser caller and required an API key.

Fix: set Origin: https://worldmonitor.app on the boundary self-fetch. This
takes the trusted-browser path without needing to embed an API key in the
probe. The probe runs edge-side with x-probe-secret internal auth; emulating
a trusted browser is only for boundary response-shape verification.

Tests still 17/17.

* fix(seed-contract-probe): explicit User-Agent on boundary self-fetch

Per AGENTS.md, server-side fetches must include a UA. middleware.ts:138
returns 403 for !ua || ua.length < 10 on non-public paths, and
/api/bootstrap is not in PUBLIC_API_PATHS — the probe works today only
because Vercel Edge implicitly adds a UA. Making it explicit.

Addresses greptile P2 on PR koala73#3100.

Author: koala73

api/seed-contract-probe.ts

@@ -163,7 +163,18 @@ const BOUNDARY_CHECKS: BoundaryCheck[] = [
 export async function checkPublicBoundary(origin: string): Promise<BoundaryResult[]> {
   return Promise.all(BOUNDARY_CHECKS.map(async ({ endpoint, requireSourceHeader }): Promise<BoundaryResult> => {
     try {
-      const r = await fetch(`${origin}${endpoint}`, { signal: AbortSignal.timeout(5_000) });
+      // Send Origin of the canonical public host so endpoints that gate
+      // behind validateApiKey() (e.g. /api/bootstrap) take the trusted-browser
+      // branch instead of demanding an API key. The probe runs edge-side with
+      // internal auth; we intentionally emulate a trusted browser for boundary
+      // verification only.
+      const r = await fetch(`${origin}${endpoint}`, {
+        signal: AbortSignal.timeout(5_000),
+        headers: {
+          Origin: 'https://worldmonitor.app',
+          'User-Agent': 'WorldMonitor-SeedContractProbe/1.0',
+        },
+      });
       const text = await r.text();
       // Detect any envelope leak in the response body. A substring match on
       // the literal `"_seed":` is sufficient because `_seed` only appears on