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/lib/routing.ts

@@ -1,7 +1,7 @@
 /**
  * Shared routing helpers for tree/session navigation.
  * Centralizes the logic for determining the correct navigation path
- * based on tree type (troubleshooting vs procedural).
+ * based on tree type (troubleshooting vs procedural vs maintenance).
  */
 
 /**
@@ -14,6 +14,9 @@ export function getTreeNavigatePath(
   if (treeType === 'procedural') {
     return `/flows/${treeId}/navigate`
   }
+  if (treeType === 'maintenance') {
+    return `/flows/${treeId}/maintenance`
+  }
   return `/trees/${treeId}/navigate`
 }
 
@@ -24,7 +27,7 @@ export function getTreeEditorPath(
   treeId: string,
   treeType?: string
 ): string {
-  if (treeType === 'procedural') {
+  if (treeType === 'procedural' || treeType === 'maintenance') {
     return `/flows/${treeId}/edit`
   }
   return `/trees/${treeId}/edit`