refactor(card onboarding): migrate to native stack (MetaMask#30707)

## **Description**
Migrate the Card Onboarding flow off the JS stack navigator and
react-navigation header in favor of native stack:

- `app/components/UI/Card/routes/OnboardingNavigator.tsx` now uses
`createNativeStackNavigator` from `@react-navigation/native-stack`
instead of `createStackNavigator`. The navigator-level header is hidden
for every screen (`headerShown: false`, `gestureEnabled: false`), so
screens own their own header chrome.


## **Changelog**

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## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: Card Onboarding header & navigation
Scenario: Back navigation on early onboarding screens
    Given I am on the Card Onboarding "Sign Up", "Confirm Email", or "Complete" screen
    When I tap the back arrow in the header
    Then the navigator goes back to the previous screen
  
Scenario: Exit with confirmation on post-email screens
    Given I am on "Set Phone Number", "Confirm Phone Number", "Verify Identity", "Personal Details", or "Physical Address"
    When I tap the close button in the header
    Then a confirmation alert appears asking me to confirm exiting onboarding
    When I confirm exit
    Then I am navigated to Wallet Home
  
Scenario: Exit directly from KYC status screen
    Given I am on the "Verifying Veriff KYC" screen
    When I tap the close button in the header
    Then I am navigated directly to Wallet Home without a confirmation alert
  
Scenario: Keyboard does not obscure inputs
    Given I am on any onboarding screen with a text input
    When I focus the input and the keyboard opens
    Then the input remains visible and the sticky action button (if any) stays above the keyboard
  
Scenario: Resume incomplete onboarding (regression)
    Given I am a returning user with incomplete onboarding
    When I re-enter the Card flow
    Then the "Keep going" modal is shown and routes me to the correct resume step
```

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**
<img width="328" height="676" alt="card onboarding before"
src="https://github.com/user-attachments/assets/81f6ec2d-e3a8-439a-9bf0-52ce4b47ae2b"
/>

### **After**
<img width="342" height="744" alt="Card Onboarding Navigation after"
src="https://github.com/user-attachments/assets/26c198bb-d39c-40b0-ace0-3de1c467965e"
/>

Android

https://github.com/user-attachments/assets/d85c4de6-514d-4186-a792-309a0e4452a2

<!-- [screenshots/recordings] -->

## **Pre-merge author checklist**

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"Ready for review". A checked box means you deliberately considered that
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Unchecked boxes are ambiguous: they are not an implicit "N/A" and they
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- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

#### Performance checks (if applicable)

- [x] I've tested on Android
  - Ideally on a mid-range device; emulator is acceptable
- [ ] I've tested with a power user scenario
- Use these [power-user
SRPs](https://consensyssoftware.atlassian.net/wiki/spaces/TL1/pages/edit-v2/401401446401?draftShareId=9d77e1e1-4bdc-4be1-9ebb-ccd916988d93)
to import wallets with many accounts and tokens
- [ ] I've instrumented key operations with Sentry traces for production
performance metrics
- See [`trace()`](/app/util/trace.ts) for usage and
[`addToken`](/app/components/Views/AddAsset/components/AddCustomToken/AddCustomToken.tsx#L274)
for an example

For performance guidelines and tooling, see the [Performance
Guide](https://consensyssoftware.atlassian.net/wiki/spaces/TL1/pages/400085549067/Performance+Guide+for+Engineers).

## **Pre-merge reviewer checklist**

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checklist: an
unchecked box is ambiguous, a checked box means the reviewer consciously
assessed that responsibility. See `docs/readme/ready-for-review.md`.
-->

- [x] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [x] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

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Author: weitingsun

app/components/UI/Card/routes/OnboardingNavigator.test.tsx

@@ -53,11 +53,11 @@ jest.mock('@react-navigation/native', () => {
   };
 });
 
-// Mock @react-navigation/stack
-jest.mock('@react-navigation/stack', () => {
+// Mock @react-navigation/native-stack
+jest.mock('@react-navigation/native-stack', () => {
   const { View } = jest.requireActual('react-native');
   return {
-    createStackNavigator: () => ({
+    createNativeStackNavigator: () => ({
       Navigator: ({
         children,
         ...props

app/components/UI/Card/routes/OnboardingNavigator.tsx

@@ -1,8 +1,8 @@
 import React, { useEffect, useMemo, useRef, useState } from 'react';
 import {
-  createStackNavigator,
-  StackNavigationOptions,
-} from '@react-navigation/stack';
+  createNativeStackNavigator,
+  NativeStackNavigationOptions,
+} from '@react-navigation/native-stack';
 import Routes from '../../../../constants/navigation/Routes';
 import SignUp from '../components/Onboarding/SignUp';
 import ConfirmEmail from '../components/Onboarding/ConfirmEmail';
@@ -27,10 +27,10 @@ import { CardUserPhase } from '../types';
 import Complete from '../components/Onboarding/Complete';
 import LockManagerService from '../../../../core/LockManagerService';
 
-const Stack = createStackNavigator();
+const Stack = createNativeStackNavigator();
 
 // All onboarding screens render HeaderStandard in-screen via OnboardingStep.
-const onboardingScreenOptions: StackNavigationOptions = {
+const onboardingScreenOptions: NativeStackNavigationOptions = {
   headerShown: false,
   gestureEnabled: false,
 };