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/src/__tests__/ui/Select.test.tsx

@@ -0,0 +1,45 @@
+import React from 'react';
+import { describe, it, expect } from 'vitest';
+import { render, screen, fireEvent } from '@testing-library/react';
+import { Select } from '@/components/ui/Select';
+
+const options = [
+  { value: 'de', label: 'Deutsch' },
+  { value: 'en', label: 'English' },
+];
+
+describe('Select', () => {
+  it('renders label and options', () => {
+    render(<Select label="Sprache" options={options} />);
+    expect(screen.getByText('Sprache')).toBeInTheDocument();
+    expect(screen.getByText('Deutsch')).toBeInTheDocument();
+    expect(screen.getByText('English')).toBeInTheDocument();
+  });
+
+  it('renders error with role=alert', () => {
+    render(<Select label="Sprache" options={options} error="Bitte auswählen" />);
+    expect(screen.getByRole('alert')).toHaveTextContent('Bitte auswählen');
+  });
+
+  it('renders helper text', () => {
+    render(<Select label="Sprache" options={options} helperText="Wählen Sie eine Sprache" />);
+    expect(screen.getByText('Wählen Sie eine Sprache')).toBeInTheDocument();
+  });
+
+  it('calls onChange when value changes', () => {
+    const onChange = vi.fn();
+    render(<Select label="Sprache" options={options} onChange={onChange} />);
+    fireEvent.change(screen.getByLabelText(/Sprache/), { target: { value: 'en' } });
+    expect(onChange).toHaveBeenCalled();
+  });
+
+  it('has min-h-touch for 44px target', () => {
+    render(<Select label="Sprache" options={options} />);
+    expect(screen.getByLabelText(/Sprache/).className).toContain('min-h-touch');
+  });
+
+  it('sets aria-required when required', () => {
+    render(<Select label="Sprache" options={options} required />);
+    expect(screen.getByLabelText(/Sprache/)).toHaveAttribute('aria-required', 'true');
+  });
+});