feat(backups): Add backup import API and improve backup download/import flow in UI

ui/src/app/core/services/api.service.ts

@@ -243,6 +243,45 @@ export class ApiService {
     return `/api/backups/${backupId}/download`;
   }
 
+  async downloadBackup(backupId: number, filename: string): Promise<void> {
+    const token = localStorage.getItem('onebox_token');
+    const response = await fetch(`/api/backups/${backupId}/download`, {
+      headers: token ? { Authorization: `Bearer ${token}` } : {},
+    });
+    if (!response.ok) {
+      throw new Error('Download failed');
+    }
+    const blob = await response.blob();
+    const url = URL.createObjectURL(blob);
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = filename;
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    URL.revokeObjectURL(url);
+  }
+
+  async importBackupFromFile(file: File, newServiceName?: string): Promise<IApiResponse<IRestoreResult>> {
+    const formData = new FormData();
+    formData.append('file', file);
+    if (newServiceName) {
+      formData.append('newServiceName', newServiceName);
+    }
+    return firstValueFrom(
+      this.http.post<IApiResponse<IRestoreResult>>('/api/backups/import', formData)
+    );
+  }
+
+  async importBackupFromUrl(url: string, newServiceName?: string): Promise<IApiResponse<IRestoreResult>> {
+    return firstValueFrom(
+      this.http.post<IApiResponse<IRestoreResult>>('/api/backups/import', {
+        url,
+        newServiceName,
+      })
+    );
+  }
+
   async restoreBackup(backupId: number, options: IRestoreOptions): Promise<IApiResponse<IRestoreResult>> {
     return firstValueFrom(
       this.http.post<IApiResponse<IRestoreResult>>('/api/backups/restore', {