chore: Next.js-Grundgerüst mit AdminLTE-CSS und Bootstrap Icons (#001)

Next.js 16 (App Router, TypeScript strict), admin-lte 4.9.1 (nur CSS),
bootstrap 5.3.8, bootstrap-icons, zod. Version 0.1.0-dev.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/app/layout.tsx

@@ -0,0 +1,17 @@
+import type { Metadata } from "next";
+import "admin-lte/dist/css/adminlte.css";
+import "bootstrap-icons/font/bootstrap-icons.css";
+import "./globals.css";
+
+export const metadata: Metadata = {
+  title: "ProxLedger",
+  description: "Proxmox Subscription Dashboard",
+};
+
+export default function RootLayout({ children }: Readonly<{ children: React.ReactNode }>) {
+  return (
+    <html lang="de">
+      <body>{children}</body>
+    </html>
+  );
+}