fix(landing): call API origin directly from Contact Sales form (#3054)

The form posted to a relative `/api/contact-sales`, which on the
Vercel-hosted web app gets handled by the `/api/*` rewrite using
the server-only `REMOTE_API_URL`. On `multica-app.copilothub.ai`
that env points at a privately-resolvable host, so the rewrite
returns 404 (`DNS_HOSTNAME_RESOLVED_PRIVATE`) even though every
other API call works — the rest of the app uses
`NEXT_PUBLIC_API_URL` and hits the API origin directly.

Switch the form to do the same: `${NEXT_PUBLIC_API_URL}/api/contact-sales`,
falling back to a relative URL for local dev / self-hosted setups
where same-origin still works.

MUL-2493

Co-authored-by: multica-agent <github@multica.ai>

apps/web/features/landing/components/contact-sales-page-client.tsx

@@ -89,7 +89,13 @@ export function ContactSalesPageClient() {
     setState({ status: "submitting" });
 
     try {
-      const res = await fetch("/api/contact-sales", {
+      // Call the API origin directly (same as the rest of the web app via
+      // `apiBaseUrl={process.env.NEXT_PUBLIC_API_URL}`). The `/api/*` Vercel
+      // rewrite uses server-only `REMOTE_API_URL`, which on Vercel may not
+      // be publicly resolvable — relying on it makes this endpoint 404 even
+      // when every other API works.
+      const apiBase = process.env.NEXT_PUBLIC_API_URL ?? "";
+      const res = await fetch(`${apiBase}/api/contact-sales`, {
         method: "POST",
         headers: { "Content-Type": "application/json" },
         body: JSON.stringify({