feat(05-01): wire BackendSelectionStep to registry and remove dead export

- Replace hardcoded BACKENDS array with Object.entries(BACKEND_REGISTRY)
- Import BACKEND_REGISTRY in BackendSelectionStep.tsx
- Remove BackendFormValues<T> export from schemas/index.ts (dead code TECH-04)
- TypeScript compiles with zero errors

src/components/wizard/BackendSelectionStep.tsx

@@ -4,6 +4,7 @@ import { zodResolver } from '@hookform/resolvers/zod';
 import { z } from 'zod';
 import { useWizard } from '../../store/context';
 import type { BackendType } from '../../store/types';
+import { BACKEND_REGISTRY } from '../../schemas/registry';
 import { BackendCard } from '../ui/BackendCard';
 
 const remoteNameSchema = z.object({
@@ -18,23 +19,6 @@ const remoteNameSchema = z.object({
 
 type RemoteNameFormValues = z.infer<typeof remoteNameSchema>;
 
-const BACKENDS: { type: BackendType; name: string; description: string }[] = [
-  {
-    type: 'azureblob',
-    name: 'Azure Blob Storage',
-    description: 'Microsoft Azure cloud storage',
-  },
-  {
-    type: 's3',
-    name: 'Amazon S3',
-    description: 'AWS Simple Storage Service',
-  },
-  {
-    type: 's3-compatible',
-    name: 'S3-Compatible',
-    description: 'Wasabi, MinIO, Cloudflare R2, and others',
-  },
-];
 
 export function BackendSelectionStep() {
   const { state, dispatch } = useWizard();
@@ -77,13 +61,13 @@ export function BackendSelectionStep() {
           )}
         </div>
         <div data-testid="backend-cards">
-          {BACKENDS.map((backend) => (
+          {Object.entries(BACKEND_REGISTRY).map(([type, entry]) => (
             <BackendCard
-              key={backend.type}
-              name={backend.name}
-              description={backend.description}
-              selected={state.remote.backendType === backend.type}
-              onClick={() => handleCardClick(backend.type)}
+              key={type}
+              name={entry.displayName}
+              description={entry.description}
+              selected={state.remote.backendType === type}
+              onClick={() => handleCardClick(type as BackendType)}
             />
           ))}
         </div>