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/vite.config.ts

@@ -0,0 +1,33 @@
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+import { resolve } from 'path';
+
+export default defineConfig({
+  plugins: [react()],
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, 'src'),
+    },
+  },
+  server: {
+    port: 5173,
+    proxy: {
+      '/api': {
+        target: 'http://localhost:8000',
+        changeOrigin: true,
+      },
+    },
+  },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: 'src/test/setup.ts',
+    css: true,
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json-summary'],
+      include: ['src/**/*.{ts,tsx}'],
+      exclude: ['src/test/**', 'src/**/*.d.ts', 'src/main.tsx'],
+    },
+  },
+});