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/components/docs/docs-shell.tsx

@@ -0,0 +1,53 @@
+"use client";
+
+import Link from "next/link";
+import { useTranslation } from "react-i18next";
+
+import { AdminLanguageSwitcher } from "@/components/admin/admin-language-switcher";
+import { cn } from "@/lib/utils";
+
+type DocsShellProps = {
+  children: React.ReactNode;
+  className?: string;
+};
+
+export function DocsShell({ children, className }: DocsShellProps): React.ReactElement {
+  const { t } = useTranslation("integrationDocs");
+
+  return (
+    <div className={cn("min-h-dvh bg-background text-foreground", className)}>
+      <header className="sticky top-0 z-40 border-b border-border/80 bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/80">
+        <div className="mx-auto flex h-14 max-w-6xl items-center justify-between gap-4 px-4 sm:px-6 lg:px-8">
+          <Link href="/docs/integration" className="truncate text-sm font-semibold tracking-tight">
+            {t("shell.title")}
+          </Link>
+          <div className="flex items-center gap-2">
+            <AdminLanguageSwitcher />
+            <Link
+              href="/admin/login"
+              className="text-xs text-muted-foreground transition-colors hover:text-foreground"
+            >
+              {t("shell.admin")}
+            </Link>
+          </div>
+        </div>
+      </header>
+      {children}
+    </div>
+  );
+}
+
+export function DocsBody({
+  sidebar,
+  children,
+}: {
+  sidebar?: React.ReactNode;
+  children: React.ReactNode;
+}): React.ReactElement {
+  return (
+    <div className="mx-auto flex w-full max-w-6xl flex-col gap-6 px-4 py-6 sm:px-6 lg:flex-row lg:gap-8 lg:px-8 lg:py-8">
+      {sidebar}
+      <main className="min-w-0 flex-1 pb-12">{children}</main>
+    </div>
+  );
+}