feat(05-03): migrate BackendSelectionStep.test.tsx from fireEvent to userEvent

- Replace fireEvent import with userEvent from @testing-library/user-event
- Add const user = userEvent.setup() inside each test body using interactions
- Replace fireEvent.click(azureButton) with await user.click(azureButton)
- Replace fireEvent.change(nameInput) with await user.clear() + await user.type()
- Make all interaction tests async

src/components/wizard/BackendSelectionStep.test.tsx

@@ -2,7 +2,8 @@
 // Covers WIZD-01: card grid renders Azure Blob, Amazon S3, S3-Compatible (Azure first)
 // Covers WIZD-04: remote name field validates alphanumeric/dash/underscore
 import { describe, it, expect } from 'vitest';
-import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+import { render, screen, waitFor } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
 import { WizardProvider } from '../../store/context';
 import { BackendSelectionStep } from './BackendSelectionStep';
 
@@ -42,16 +43,18 @@ describe('BackendSelectionStep', () => {
       expect(azureIdx).toBeLessThan(s3Idx);
     });
 
-    it('clicking a backend card dispatches SET_BACKEND_TYPE and SET_STEP', () => {
+    it('clicking a backend card dispatches SET_BACKEND_TYPE and SET_STEP', async () => {
+      const user = userEvent.setup();
       renderStep();
       // Fill in a valid remote name first
       const nameInput = screen.getByRole('textbox');
-      fireEvent.change(nameInput, { target: { value: 'my-remote' } });
+      await user.clear(nameInput);
+      await user.type(nameInput, 'my-remote');
       // Click the Azure card — if navigation dispatches SET_STEP(1), component may unmount
       // We verify no validation error appears (meaning dispatch proceeded)
       const azureButton = screen.getAllByRole('button').find(b => b.textContent?.includes('Azure Blob Storage'))!;
       expect(azureButton).toBeDefined();
-      fireEvent.click(azureButton);
+      await user.click(azureButton);
       // After successful navigation step fires, no validation alert should be present
       expect(screen.queryByRole('alert')).toBeNull();
     });
@@ -77,10 +80,11 @@ describe('BackendSelectionStep', () => {
     });
 
     it('shows inline error after first Next attempt with invalid name', async () => {
+      const user = userEvent.setup();
       renderStep();
       // Click a card without filling in name — triggers validation
       const azureButton = screen.getAllByRole('button').find(b => b.textContent?.includes('Azure Blob Storage'))!;
-      fireEvent.click(azureButton);
+      await user.click(azureButton);
       // Error should appear after async validation
       await waitFor(() => {
         expect(screen.getByRole('alert')).toBeDefined();
@@ -89,11 +93,13 @@ describe('BackendSelectionStep', () => {
     });
 
     it('accepts alphanumeric, dashes, and underscores', async () => {
+      const user = userEvent.setup();
       renderStep();
       const nameInput = screen.getByRole('textbox');
-      fireEvent.change(nameInput, { target: { value: 'my-remote_01' } });
+      await user.clear(nameInput);
+      await user.type(nameInput, 'my-remote_01');
       const azureButton = screen.getAllByRole('button').find(b => b.textContent?.includes('Azure Blob Storage'))!;
-      fireEvent.click(azureButton);
+      await user.click(azureButton);
       // Valid name — no alert should appear (wait briefly to confirm no error appears)
       await waitFor(() => {
         expect(screen.queryByRole('alert')).toBeNull();
@@ -101,11 +107,13 @@ describe('BackendSelectionStep', () => {
     });
 
     it('rejects names with spaces or special characters', async () => {
+      const user = userEvent.setup();
       renderStep();
       const nameInput = screen.getByRole('textbox');
-      fireEvent.change(nameInput, { target: { value: 'my remote!' } });
+      await user.clear(nameInput);
+      await user.type(nameInput, 'my remote!');
       const azureButton = screen.getAllByRole('button').find(b => b.textContent?.includes('Azure Blob Storage'))!;
-      fireEvent.click(azureButton);
+      await user.click(azureButton);
       // Invalid name — alert should appear after async validation
       await waitFor(() => {
         expect(screen.getByRole('alert')).toBeDefined();