feat(backup): add enterprise backup & restore foundation

frontend/athena/types/backup.ts

@@ -0,0 +1,49 @@
+export interface BackupManifest {
+  backup_id: string;
+  created_at: string;
+  app_version: string;
+  backup_type: string;
+  database_url_host_anonymized: string;
+  database_name: string;
+  storage_base_path: string;
+  included_sections: string[];
+  file_count: number;
+  total_size_bytes: number;
+  checksum_sha256: string;
+  created_by_user_id: number | null;
+  created_by_username: string;
+}
+
+export interface BackupSummary {
+  filename: string;
+  size_bytes: number;
+  created_at: string | null;
+  app_version: string;
+  backup_type: string;
+  database_name: string;
+  storage_base_path: string;
+  file_count: number;
+  total_size_bytes: number;
+  created_by_user_id: number | null;
+  created_by_username: string;
+  validation_status: string;
+  validation_message: string;
+}
+
+export interface BackupListResponse {
+  items: BackupSummary[];
+  total_count: number;
+  total_size_bytes: number;
+  latest_backup_at: string | null;
+}
+
+export interface BackupValidationResponse {
+  filename: string;
+  valid: boolean;
+  message: string;
+  issues: string[];
+  checksum_valid: boolean;
+  restore_supported: boolean;
+  requires_cli_restore: boolean;
+  manifest: BackupManifest | null;
+}