feat(01-01): Next.js app + Docker Compose stack with network segmentation

- Next.js 15 app with Tailwind CSS v4, standalone output for Docker
- Root layout with de locale, page with Tessera placeholder
- Multi-stage Dockerfile for web with monorepo root context
- Docker Compose with 4 services: traefik, web, api, db
- Three segregated networks: frontend-net, backend-net, data-net (internal)
- Traefik v2.11 reverse proxy routing / to web, /api to api
- API strip prefix middleware for clean routing
- PostgreSQL 16-alpine with health checks and named volume
- Fixed API Dockerfile for pnpm monorepo node_modules structure
- Fixed Next.js standalone path for monorepo (apps/web/server.js)
- Fixed Traefik Docker API version compatibility
- Network segmentation: web NOT on data-net, api NOT on frontend-net

apps/web/src/app/layout.tsx

@@ -0,0 +1,21 @@
+import type { Metadata } from 'next';
+import './globals.css';
+
+export const metadata: Metadata = {
+  title: 'Tessera',
+  description: 'Modulare Workflow-Plattform',
+};
+
+export default function RootLayout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  return (
+    <html lang="de">
+      <body className="antialiased">
+        {children}
+      </body>
+    </html>
+  );
+}