fix(admin): sidebar invisible (CSS specificity) + /admin lands on dashboard

- AdminShell: the rtl:/ltr: translate variants ([dir] selector) out-specified
  lg:translate-x-0, so the sidebar stayed off-screen on desktop and the mobile
  drawer couldn't open. Pin physically right + plain translate-x-full/0; content
  uses lg:mr-60.
- /admin now redirects to /admin/stats (overview) instead of /admin/nodes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/[locale]/admin/page.tsx

@@ -1,5 +1,6 @@
 import { redirect } from "next/navigation";
 
 export default function AdminRootPage() {
-  redirect("/admin/nodes");
+  // Land on the dashboard overview, not an arbitrary section.
+  redirect("/admin/stats");
 }