feat(frontend): add API client, layout, and routing

- Create Axios-based API client with sources, jobs, and dashboard endpoints
- Add responsive Layout component with navigation sidebar
- Set up React Router with Dashboard, Backups, and Settings routes
- Configure TanStack Query provider with default options
- Use lucide-react for navigation icons

frontend/src/api/client.ts

@@ -0,0 +1,61 @@
+import axios from 'axios';
+
+const API_BASE_URL = '/api';
+
+export const apiClient = axios.create({
+  baseURL: API_BASE_URL,
+  headers: {
+    'Content-Type': 'application/json',
+  },
+});
+
+export interface BackupSource {
+  id: string;
+  name: string;
+  type: string;
+  config: Record<string, unknown>;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface BackupJob {
+  id: string;
+  source_id: string;
+  status: 'pending' | 'running' | 'completed' | 'failed';
+  started_at: string | null;
+  completed_at: string | null;
+  error_message: string | null;
+  created_at: string;
+}
+
+export interface DashboardStats {
+  total_sources: number;
+  total_jobs: number;
+  completed_jobs: number;
+  failed_jobs: number;
+  pending_jobs: number;
+}
+
+export const sourcesApi = {
+  getAll: () => apiClient.get<BackupSource[]>('/sources'),
+  getById: (id: string) => apiClient.get<BackupSource>(`/sources/${id}`),
+  create: (data: Omit<BackupSource, 'id' | 'created_at' | 'updated_at'>) =>
+    apiClient.post<BackupSource>('/sources', data),
+  update: (id: string, data: Partial<BackupSource>) =>
+    apiClient.put<BackupSource>(`/sources/${id}`, data),
+  delete: (id: string) => apiClient.delete(`/sources/${id}`),
+};
+
+export const jobsApi = {
+  getAll: () => apiClient.get<BackupJob[]>('/jobs'),
+  getById: (id: string) => apiClient.get<BackupJob>(`/jobs/${id}`),
+  create: (sourceId: string) =>
+    apiClient.post<BackupJob>('/jobs', { source_id: sourceId }),
+  getLogs: (id: string) => apiClient.get<string>(`/jobs/${id}/logs`),
+};
+
+export const dashboardApi = {
+  getStats: () => apiClient.get<DashboardStats>('/dashboard/stats'),
+  getRecentJobs: (limit: number = 10) =>
+    apiClient.get<BackupJob[]>(`/dashboard/recent-jobs?limit=${limit}`),
+};