feat(T01): auth + user management + RBAC + base frontend + i18n

- Backend: FastAPI, JWT auth (HS256), bcrypt, RBAC middleware
- User CRUD (admin-only), soft-delete, pagination
- Pydantic BaseSettings config, async SQLAlchemy 2.0
- 50 backend tests, 88% coverage
- Frontend: Next.js 14 App Router, Tailwind, design tokens
- Login page, auth context, API client with auto-refresh
- i18n: next-intl, DE/EN (31 keys each)
- 6 base UI components (Button, Input, Card, Table, Modal, Toast)
- 12 frontend tests, npm build success

frontend/next.config.js

@@ -0,0 +1,11 @@
+const { NextConfig } = require('next');
+
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  reactStrictMode: true,
+  env: {
+    NEXT_PUBLIC_API_URL: process.env.NEXT_PUBLIC_API_URL || 'http://localhost:8000/api/v1',
+  },
+};
+
+module.exports = nextConfig;