feat(03-03): implement BackendSelectionStep (WIZD-01, WIZD-04)

- Remote name field with zod validation (mode: onSubmit, reValidateMode: onChange)
- Three backend cards in popularity order: Azure Blob, Amazon S3, S3-Compatible
- Card click validates name first; dispatches SET_REMOTE_NAME + SET_BACKEND_TYPE + SET_REMOTE_PARAMS({}) + SET_STEP(1)
- Does NOT dispatch RESET — preserves deployment options
- All 10 BackendSelectionStep tests GREEN

src/components/wizard/BackendSelectionStep.test.tsx

@@ -2,7 +2,7 @@
 // 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 } from '@testing-library/react';
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
 import { WizardProvider } from '../../store/context';
 import { BackendSelectionStep } from './BackendSelectionStep';
 
@@ -76,35 +76,41 @@ describe('BackendSelectionStep', () => {
       expect(screen.queryByRole('alert')).toBeNull();
     });
 
-    it('shows inline error after first Next attempt with invalid name', () => {
+    it('shows inline error after first Next attempt with invalid name', async () => {
       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);
-      // Error should appear
-      expect(screen.getByRole('alert')).toBeDefined();
-      expect(screen.getByText(/required/i)).toBeDefined();
+      // Error should appear after async validation
+      await waitFor(() => {
+        expect(screen.getByRole('alert')).toBeDefined();
+        expect(screen.getByText(/required/i)).toBeDefined();
+      });
     });
 
-    it('accepts alphanumeric, dashes, and underscores', () => {
+    it('accepts alphanumeric, dashes, and underscores', async () => {
       renderStep();
       const nameInput = screen.getByRole('textbox');
       fireEvent.change(nameInput, { target: { value: 'my-remote_01' } });
       const azureButton = screen.getAllByRole('button').find(b => b.textContent?.includes('Azure Blob Storage'))!;
       fireEvent.click(azureButton);
-      // Valid name — no alert should appear
-      expect(screen.queryByRole('alert')).toBeNull();
+      // Valid name — no alert should appear (wait briefly to confirm no error appears)
+      await waitFor(() => {
+        expect(screen.queryByRole('alert')).toBeNull();
+      });
     });
 
-    it('rejects names with spaces or special characters', () => {
+    it('rejects names with spaces or special characters', async () => {
       renderStep();
       const nameInput = screen.getByRole('textbox');
       fireEvent.change(nameInput, { target: { value: 'my remote!' } });
       const azureButton = screen.getAllByRole('button').find(b => b.textContent?.includes('Azure Blob Storage'))!;
       fireEvent.click(azureButton);
-      // Invalid name — alert should appear
-      expect(screen.getByRole('alert')).toBeDefined();
-      expect(screen.getByText(/letters, numbers, dashes/i)).toBeDefined();
+      // Invalid name — alert should appear after async validation
+      await waitFor(() => {
+        expect(screen.getByRole('alert')).toBeDefined();
+        expect(screen.getByText(/letters, numbers, dashes/i)).toBeDefined();
+      });
     });
   });
 });