feat(06-03): extend RemoteConfigStep for all 7 backends

- Add SftpAuthToggle import
- Extend backendLabel record to cover onedrive/sftp/gcs/b2
- Add sftp branch with host/user FieldRenderers + SftpAuthToggle
- onedrive/gcs/b2 render via existing registry loop (no custom branch)
- Full Vitest suite green (147 tests); zero TypeScript errors

src/components/wizard/RemoteConfigStep.tsx

@@ -9,6 +9,7 @@ import { BACKEND_REGISTRY } from '../../schemas/registry';
 import { BACKEND_SCHEMAS } from '../../schemas';
 import { FieldRenderer } from '../ui/FieldRenderer';
 import { AzureAuthToggle } from './AzureAuthToggle';
+import { SftpAuthToggle } from './SftpAuthToggle';
 import type { FieldError } from 'react-hook-form';
 
 export function RemoteConfigStep() {
@@ -45,6 +46,10 @@ export function RemoteConfigStep() {
     azureblob:       'Azure Blob Storage',
     s3:              'Amazon S3',
     's3-compatible': 'S3-Compatible Storage',
+    onedrive:        'OneDrive',
+    sftp:            'SFTP',
+    gcs:             'Google Cloud Storage',
+    b2:              'Backblaze B2',
   };
 
   return (
@@ -68,8 +73,30 @@ export function RemoteConfigStep() {
               }}
             />
           </>
+        ) : backendType === 'sftp' ? (
+          <>
+            {/* host and user via FieldRenderer */}
+            <FieldRenderer
+              field={BACKEND_REGISTRY.sftp.fields.find(f => f.key === 'host')!}
+              register={register}
+              error={errors.host as FieldError | undefined}
+            />
+            <FieldRenderer
+              field={BACKEND_REGISTRY.sftp.fields.find(f => f.key === 'user')!}
+              register={register}
+              error={errors.user as FieldError | undefined}
+            />
+            {/* Auth toggle handles pass + key_pem — both always registered */}
+            <SftpAuthToggle
+              register={register}
+              errors={{
+                pass: errors.pass as FieldError | undefined,
+                key_pem: errors.key_pem as FieldError | undefined,
+              }}
+            />
+          </>
         ) : (
-          /* S3 and S3-compatible: full registry loop — FieldRenderer handles provider hiding */
+          /* All others (onedrive, gcs, b2, s3, s3-compatible): full registry loop */
           BACKEND_REGISTRY[backendType].fields.map(field => (
             <FieldRenderer
               key={field.key}