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/components/ui/ConfirmDialog.tsx

@@ -0,0 +1,42 @@
+import React from 'react';
+import { Modal } from './Modal';
+import { Button } from './Button';
+import { useTranslation } from 'react-i18next';
+
+export interface ConfirmDialogProps {
+  open: boolean;
+  title?: string;
+  message: string;
+  confirmLabel?: string;
+  cancelLabel?: string;
+  variant?: 'primary' | 'danger';
+  onConfirm: () => void;
+  onCancel: () => void;
+}
+
+export function ConfirmDialog({
+  open,
+  title,
+  message,
+  confirmLabel,
+  cancelLabel,
+  variant = 'primary',
+  onConfirm,
+  onCancel,
+}: ConfirmDialogProps) {
+  const { t } = useTranslation();
+
+  return (
+    <Modal open={open} onClose={onCancel} title={title || t('confirmDialog.title')} size="sm">
+      <p className="text-sm text-secondary-700">{message}</p>
+      <div className="mt-6 flex justify-end gap-3">
+        <Button variant="secondary" onClick={onCancel}>
+          {cancelLabel || t('confirmDialog.cancel')}
+        </Button>
+        <Button variant={variant === 'danger' ? 'danger' : 'primary'} onClick={onConfirm}>
+          {confirmLabel || t('confirmDialog.confirm')}
+        </Button>
+      </div>
+    </Modal>
+  );
+}