test: dedup sonner mocks and close Toolbar seam-mock gaps

- Replace 10 inline sonner toast mocks with the shared mockSonner() builder.
- Toolbar: add tests for the store-driven undo/redo disabled state and the
  unsaved-changes dot — behaviour the full-store mock previously left
  unasserted.

ha-relevant: yes

frontend/src/components/zwave/__tests__/ZwaveImportModal.test.tsx

@@ -9,7 +9,7 @@ vi.mock('@/api/client', () => ({
     importToPending: vi.fn(),
   },
 }))
-vi.mock('sonner', () => ({ toast: { success: vi.fn(), error: vi.fn(), info: vi.fn() } }))
+vi.mock('sonner', async () => (await import('@/test/mocks')).mockSonner())
 
 import { zwaveApi } from '@/api/client'
 import { toast } from 'sonner'