fix: resolve CI failures — ESLint unused vars and AI chat tests in CI

Frontend: suppress unused-vars ESLint errors for callback params in
MaintenanceFlowDetailPage and StepLibraryPage.

Backend: add autouse fixture to mock settings.ai_enabled=True in
test_ai_chat.py so tests pass in CI where no ANTHROPIC_API_KEY is set.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/MaintenanceFlowDetailPage.tsx

@@ -66,6 +66,7 @@ export default function MaintenanceFlowDetailPage() {
     load()
   }, [id, navigate])
 
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
   const handleLaunched = (batchId: string, _count: number) => {
     setShowBatchModal(false)
     setBannerDismissed(false)

frontend/src/pages/StepLibraryPage.tsx

@@ -73,6 +73,7 @@ export default function StepLibraryPage() {
     }
   }
 
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
   const handleFormSuccess = (_step: Step) => {
     setCreateOpen(false)
     setEditingStep(null)