feat: 1.7 new srp welcome back

[ieow]

Description

1.7
Update New SRP onboarding flow as per figma design
https://www.figma.com/design/pViOUcmjwhEzFsdrwknpNc/Onboarding-redesign?node-id=434-55200&t=wmEoQSF9g9lFtkwp-0

This PR is part 7 of 9 for the new SRP ui update

This PR cover

• new ui welcome back screen ( Login Screen)

Related issues

Fixes:

Manual testing steps

1. Go to this page...

Screenshots/Recordings

Before

After

Screen.Recording.2025-05-24.at.5.30.13.PM.mov

Pre-merge author checklist

• I’ve followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). 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.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[smgv]

I have read the CLA Document and I hereby sign the CLA