[native] use HeaderBackButton in QR Auth Flow to support light theme

Summary:
Part of [ENG-9959](https://linear.app/comm/issue/ENG-9959/improve-scanning-qr-code-flow).

Tracked in [ENG-10025](https://linear.app/comm/issue/ENG-10025/make-qr-flow-darklight-theme-consistent-with-registration-flow).

Note: The copy needs to be updated, I need to rebase the stack

Example:
{F3481493}

Depends on D14161

Test Plan: Test flow in light mode

Reviewers: ashoat, tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D14162

native/account/qr-auth/qr-auth-navigator.react.js

@@ -14,6 +14,7 @@ import QRAuthNotPrimaryDevice from './qr-auth-not-primary-device.react.js';
 import SecondaryDeviceConnected from './secondary-device-connected.react.js';
 import SecondaryDeviceNotResponding from './secondary-device-not-responding.react.js';
 import SecondaryDeviceQRCodeScanner from './secondary-device-qr-code-scanner.react.js';
+import HeaderBackButton from '../../navigation/header-back-button.react.js';
 import HeaderCloseLeftButton from '../../navigation/header-close-left-button.react.js';
 import type { RootNavigationProp } from '../../navigation/root-navigator.react.js';
 import {
@@ -70,6 +71,9 @@ const disableGesturesScreenOptions = {
   headerLeft: null,
   gestureEnabled: false,
 };
+const overrideHeaderBackButton = {
+  headerLeft: HeaderBackButton,
+};
 
 // eslint-disable-next-line no-unused-vars
 function QRAuthNavigator(props: Props): React.Node {
@@ -84,10 +88,12 @@ function QRAuthNavigator(props: Props): React.Node {
         <QRAuthStack.Screen
           name={QRAuthNotPrimaryDeviceRouteName}
           component={QRAuthNotPrimaryDevice}
+          options={overrideHeaderBackButton}
         />
         <QRAuthStack.Screen
           name={ConnectSecondaryDeviceRouteName}
           component={ConnectSecondaryDevice}
+          options={overrideHeaderBackButton}
         />
         <QRAuthStack.Screen
           name={SecondaryDeviceConnectedRouteName}