chore(runway): cherry-pick fix: rehydration login cp-7.63.0 (#25261)

- fix: rehydration login cp-7.63.0 (#25246)

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## **Description**
The new unlockWallet check for existingUser flag before proceed with
rehydration
since rehydration happen before existing flag is set, it will always not
able to rehydrate when call with unLockWallet.

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## **Changelog**

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CHANGELOG entry: null

## **Related issues**

Fixes:
#25247

## **Manual testing steps**

```gherkin
Feature: Login with rehydration

  Scenario: user login with existing social account
    Given enter password at rehydration screen
 
    Then should unlocked the wallet
```

## **Screenshots/Recordings**

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

### **Before**

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https://github.com/user-attachments/assets/da6b051f-d859-4625-9f08-d3256de85d00


### **After**

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



https://github.com/user-attachments/assets/5a313b68-8702-488c-b4a4-789e72b77a5d

## **Pre-merge author checklist**

- [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.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] 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.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Allows seedless OAuth rehydration to unlock during app start.
> 
> - Updates `unlockWallet` to treat `authPreference.oauth2Login` as an
existing user, attempting unlock even when `existingUser` is not yet set
> - Prevents blocked rehydration flows by deriving/using password and
proceeding with post-login steps
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
54718af. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->


[732c3e5](732c3e5)

Co-authored-by: ieow <4881057+ieow@users.noreply.github.com>

Author: runway-github[bot]

app/core/Authentication/Authentication.ts

@@ -765,8 +765,9 @@ class AuthenticationService {
     try {
       const existingUser = selectExistingUser(ReduxService.store.getState());
 
-      if (existingUser) {
+      if (existingUser || authPreference?.oauth2Login) {
         // User exists. Attempt to unlock wallet.
+        // existing user is always false when user try to rehydrate
 
         if (password) {
           // Explicitly provided password.