feat: update optin metrics screen ui changes (MetaMask#24008)

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## **Description**
* feat: update optin metrics screen changes.
* Jira: https://consensyssoftware.atlassian.net/browse/SL-406
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## **Changelog**

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CHANGELOG entry: Update optin metrics screen ui changes

## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]
```

## **Screenshots/Recordings**

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

### **Before**
<img width="319" height="722" alt="Screenshot 2025-12-15 at 3 17 13 PM"
src="https://github.com/user-attachments/assets/c7205498-a61a-458e-96c6-f91db02a5237"
/>

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

### **After**
<img width="324" height="728" alt="Screenshot 2025-12-15 at 1 51 41 PM"
src="https://github.com/user-attachments/assets/e5f4adb0-b0a6-4ab6-b8b2-9b27293ff33f"
/>

<img width="270" height="570" alt="Screenshot 2025-12-15 at 6 20 54 PM"
src="https://github.com/user-attachments/assets/a69225f5-71c6-4460-aab4-1567d1dff499"
/>


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

## **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]
> Updates the OptinMetrics screen layout (image above title, larger
illustration, right-aligned checkboxes, adjusted paddings) and changes
title copy to “Improve MetaMask.”
> 
> - **UI (OptinMetrics)**
> - **Layout**: Moves illustration above title; increases illustration
height to 180; adjusts container paddings (`paddingTop: 40`, split
action padding to `paddingHorizontal`/`paddingTop`).
> - **Checkbox Rows**: Switches to `justifyContent: space-between`;
places text on left and `Checkbox` on right; removes extra right margin;
maintains disabled styling logic.
> - **Button Bar**: Replaces uniform `padding` with `paddingHorizontal`
and `paddingTop`.
> - **Copy/i18n**
> - Updates `privacy_policy.description_title` from `Help improve
MetaMask` to `Improve MetaMask`.
> - **Tests**
> - Snapshot updates reflecting new layout, paddings, image size, and
title text.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
7ec03fd. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: grvgoel81