refactor: updated AI icon to the filled version (MetaMask#27273)

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## **Description**

Updates the AI icon in the component library to use the filled version
for visual consistency.

1. **Reason for the change:** The AI icon was using an outline style;
switching to the filled version aligns with design and improves
visibility/recognition.
2. **Improvement:** Replaced the AI icon asset with the filled variant.

## **Changelog**

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## **Related issues**

Fixes: https://consensyssoftware.atlassian.net/browse/DSYS-553

## **Manual testing steps**

```gherkin
Feature: AI icon display

  Scenario: AI icon shows filled variant
    Given the app is open

    When user navigates to a screen that displays the AI icon (e.g. Predict, or component library / Storybook)
    Then the AI icon is displayed in the filled style
    And the icon renders correctly at various sizes
```

## **Screenshots/Recordings**

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

### **Before**

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### **After**


https://github.com/user-attachments/assets/756a06f3-f905-4438-ba91-82eff918e842

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## **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]
> **Low Risk**
> Low risk asset-only change; impact is limited to UI rendering of the
AI icon and could only affect visual appearance or sizing.
> 
> **Overview**
> Updates the component library AI icon by swapping `assets/ai.svg` to a
filled version and adding explicit `width`/`height` attributes on the
root `<svg>` to standardize sizing.
> 
> No code logic changes; only the rendered appearance of the `ai` icon
is affected wherever it’s used.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
044d67b. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: brianacnguyen