feat: maintenance flows frontend foundation - types, API clients, sidebar, library filter

- Add maintenance.ts types: TargetEntry, TargetList, MaintenanceSchedule, BatchLaunch
- Add targetListsApi and maintenanceSchedulesApi/batchLaunchApi clients
- Extend TreeType union with 'maintenance' in tree.ts
- Update getTreeNavigatePath/getTreeEditorPath in routing.ts for maintenance
- Sidebar: track maintenance count and add Maintenance sub-nav item
- TreeLibraryPage: add maintenance to typeFilter state, URL sync, and tab buttons
- TreeGridView, TreeListView, TreeTableView: add amber Wrench maintenance badge

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/api/index.ts

@@ -13,3 +13,5 @@ export { default as adminApi } from './admin'
 export { treeMarkdownApi } from './treeMarkdown'
 export { default as pinnedFlowsApi } from './pinnedFlows'
 export { default as analyticsApi } from './analytics'
+export { targetListsApi } from './targetLists'
+export { maintenanceSchedulesApi, batchLaunchApi } from './maintenanceSchedules'