[UX] "Add contact" Button Too Small and Difficult to Use in MetaMask Extension

Nobody has claimed this yet.

## Issue Description:

The "Add contact" button in the MetaMask Extension's contacts screen is notably small and positioned awkwardly, making it difficult for users to interact with. Its current design negatively impacts usability and user experience.

### Current Behavior:

* The "Add contact" button at the bottom of the contacts list is undersized and not prominent enough.
* Users might experience difficulty accurately clicking the button, particularly on high-resolution displays or with accessibility considerations.

### Expected Behavior:

* The button should be clearly visible, easily clickable, and sufficiently sized for all users.
* Its position and size should follow UX best practices for clear navigation and usability.

### Steps to Reproduce:

1. Open MetaMask Extension.
2. Navigate to the Contacts section.
3. Scroll down to view the "Add contact" button at the bottom.
4. Observe the small size and awkward positioning.

### Environment:

* MetaMask Extension version: 13.0
* Browser: Chrome, Firefox, Brave (observed across multiple browsers)

### Screenshots:

### Suggested Solution:

* Increase the size and visibility of the "Add contact" button.
* Improve the placement and styling according to standard UI/UX design practices.

### Additional Context:

Flagged during recent UAT as impacting user experience.

Start in the MetaMask Extension contacts screen and inspect the existing "Add contact" button, its size, placement, and styling. Confirm the updated control is easy to see and click across the stated browsers and display sizes, with the contacts flow still working as expected.

Written by the indexing model from the issue text.