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/targetLists.ts

@@ -0,0 +1,19 @@
+import { apiClient } from './client'
+import type { TargetList, TargetListCreate } from '@/types'
+
+export const targetListsApi = {
+  list: (): Promise<TargetList[]> =>
+    apiClient.get('/target-lists/').then(r => r.data),
+
+  get: (id: string): Promise<TargetList> =>
+    apiClient.get(`/target-lists/${id}`).then(r => r.data),
+
+  create: (data: TargetListCreate): Promise<TargetList> =>
+    apiClient.post('/target-lists/', data).then(r => r.data),
+
+  update: (id: string, data: Partial<TargetListCreate>): Promise<TargetList> =>
+    apiClient.put(`/target-lists/${id}`, data).then(r => r.data),
+
+  delete: (id: string): Promise<void> =>
+    apiClient.delete(`/target-lists/${id}`).then(() => undefined),
+}