feat(docs, integration): update integration documentation and redirect legacy paths

Introduced a new public documentation site for client integration at `/docs` and `/docs/integration`, removing the need for admin login. Updated the integration guide to redirect from the old admin path to the new documentation site. Added localization support for the integration documentation in English, Nepali, and Chinese. Enhanced the layout structure and improved the handling of currency display in settlement bills.

src/app/docs/layout.tsx

@@ -0,0 +1,16 @@
+import type { Metadata } from "next";
+import type { ReactNode } from "react";
+
+import { DocsShell } from "@/components/docs/docs-shell";
+
+export const metadata: Metadata = {
+  title: {
+    template: "%s · Integration API",
+    default: "Integration API",
+  },
+  description: "Lottery integration docs: SSO, wallet gateway, transfers.",
+};
+
+export default function DocsLayout({ children }: { children: ReactNode }): React.ReactElement {
+  return <DocsShell>{children}</DocsShell>;
+}