T07a: frontend core SPA — shell + auth + routing + i18n + UI library + a11y

- React 18 + Vite + TypeScript + Tailwind CSS setup
- AppShell with Sidebar (plugin menu) + TopBar (tenant switcher, search, notifications, user menu)
- Auth pages: Login, PasswordResetRequest, PasswordResetConfirm
- Protected routes with auth guard
- API client (axios with interceptors: session cookie, 401 redirect, 422 validation)
- TanStack Query hooks for auth, users, companies, contacts, notifications
- Zustand stores: authStore, uiStore
- i18n setup (de/en locales) with react-i18next
- UI component library: Button, Input, Select, Modal, Toast, Table, Card, Badge, Avatar, Pagination, EmptyState, Skeleton, ConfirmDialog
- Accessibility: ARIA labels, 44px touch targets, keyboard nav, reduced-motion, sr-only
- Design tokens from prototype as CSS custom properties
- 111 tests passing across 20 test files
- tsc --noEmit: 0 errors
- npm run build: success (471KB JS, 24KB CSS)

frontend/tsconfig.node.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ES2023"],
+    "module": "ESNext",
+    "skipLibCheck": true,
+    "moduleResolution": "bundler",
+    "allowSyntheticDefaultImports": true,
+    "isolatedModules": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "strict": true
+  },
+  "include": ["vite.config.ts"]
+}