feat(11-02): auto-scroll to first errored field on validation failure

- BackendSelectionStep: add onInvalidSubmit scrolling to remote-name input
- BackendSelectionStep: pass onInvalidSubmit to form onSubmit and handleCardClick
- RemoteConfigStep: add FieldErrors import from react-hook-form
- RemoteConfigStep: add onInvalidSubmit scrolling to first errored field by key
- RemoteConfigStep: pass onInvalidSubmit to form onSubmit

src/components/wizard/BackendSelectionStep.tsx

@@ -50,9 +50,14 @@ export function BackendSelectionStep() {
     dispatch({ type: 'SET_STEP', payload: 1 });
   }
 
+  function onInvalidSubmit() {
+    // Only one validatable field in this step: remote-name
+    document.getElementById('remote-name')?.scrollIntoView({ behavior: 'smooth', block: 'center' });
+  }
+
   function handleCardClick(backendType: BackendType) {
     pendingBackend.current = backendType;
-    void handleSubmit(onValidSubmit)();
+    void handleSubmit(onValidSubmit, onInvalidSubmit)();
   }
 
   return (
@@ -62,7 +67,7 @@ export function BackendSelectionStep() {
         Name your remote and pick the cloud storage provider you want to connect to.
         Your choice determines which credentials are required in the next step.
       </p>
-      <form onSubmit={handleSubmit(onValidSubmit)}>
+      <form onSubmit={handleSubmit(onValidSubmit, onInvalidSubmit)}>
         <TextFieldMD3
           id="remote-name"
           label="Remote name"

src/components/wizard/RemoteConfigStep.tsx

@@ -10,7 +10,7 @@ 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';
+import type { FieldError, FieldErrors } from 'react-hook-form';
 import { MD3_BTN_FILLED, MD3_BTN_OUTLINED } from '../../styles/md3-buttons';
 
 export function RemoteConfigStep() {
@@ -43,6 +43,13 @@ export function RemoteConfigStep() {
     dispatch({ type: 'SET_STEP', payload: 2 });
   };
 
+  function onInvalidSubmit(errors: FieldErrors) {
+    const firstKey = Object.keys(errors)[0];
+    if (firstKey) {
+      document.getElementById(firstKey)?.scrollIntoView({ behavior: 'smooth', block: 'center' });
+    }
+  }
+
   const backendLabel: Record<NonNullable<typeof backendType>, string> = {
     azureblob:       'Azure Blob Storage',
     s3:              'Amazon S3',
@@ -60,7 +67,7 @@ export function RemoteConfigStep() {
         Enter the credentials for your selected backend. These values are written directly into the
         generated rclone.conf and are never sent to any server.
       </p>
-      <form onSubmit={handleSubmit(onNext)}>
+      <form onSubmit={handleSubmit(onNext, onInvalidSubmit)}>
         {backendType === 'azureblob' ? (
           <>
             {/* Account field via FieldRenderer */}