Add /client launcher page (auth-gated SSO ticket + embed)

Faithful to AtomCMS's NitroController: requires a session (redirects to /login),
issues + persists the SSO ticket via issueSsoTicket (auth_ticket + ip_current
from x-forwarded-for), and embeds the configured client URL with ?sso=. Ties
auth + SSO + settings together.

Verified: tsc exit 0, next build exit 0 (/client route).

src/app/client/page.tsx

@@ -0,0 +1,49 @@
+import { headers } from "next/headers";
+import { redirect } from "next/navigation";
+import { issueSsoTicket } from "@/lib/auth/sso-ticket";
+import { auth } from "@/lib/auth";
+import { prisma } from "@/lib/prisma";
+import { siteSettings } from "@/lib/services/site-settings";
+
+export const dynamic = "force-dynamic";
+
+export default async function ClientPage() {
+  const session = await auth();
+  if (!session?.user?.id) redirect("/login");
+
+  const userId = Number(session.user.id);
+  const [hotelName, clientUrl] = await Promise.all([
+    siteSettings.get("hotel_name", "Atom"),
+    siteSettings.get("nitro_client_url", ""),
+  ]);
+
+  const hdrs = await headers();
+  const ip =
+    hdrs.get("x-forwarded-for")?.split(",")[0]?.trim() ?? hdrs.get("x-real-ip") ?? "0.0.0.0";
+
+  // Faithful to AtomCMS's NitroController: issue (and persist) the SSO ticket on
+  // the launcher render, then hand it to the client.
+  const ticket = await issueSsoTicket(prisma, userId, hotelName ?? "Atom", ip);
+
+  const src = clientUrl
+    ? `${clientUrl}${clientUrl.includes("?") ? "&" : "?"}sso=${encodeURIComponent(ticket)}`
+    : "";
+
+  return (
+    <main>
+      <h1>Launching {hotelName ?? "Atom"}…</h1>
+      {src ? (
+        <iframe
+          title="Hotel client"
+          src={src}
+          style={{ width: "100%", height: "80vh", border: 0, borderRadius: 10 }}
+        />
+      ) : (
+        <p className="muted">
+          No client URL configured (set <code>nitro_client_url</code> in settings). SSO ticket
+          issued for this session: <code>{ticket}</code>
+        </p>
+      )}
+    </main>
+  );
+}