Replace title gen screenshots with gif

[jeffpaul]

What?

This pull request updates the screenshots section in the plugin's readme.txt file to better reflect the current user interface and streamline the descriptions for the title gen experiment.

Readme and documentation updates:

• Combined the descriptions of the generate and re-generate title features, and condensed the screenshots list to match the latest UI, removing redundant or outdated entries.

Why?

How?

Testing Instructions

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: jeffpaul <[email protected]>
Co-authored-by: dkotter <[email protected]>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.