feat: add stop/cancel execution control for agents

[ishaannk]

Description

Brief description of the changes in this PR.

Closes #5118

Summary

Implemented stop and cancel execution control for agents.

Changes

• Added stop execution mechanism
• Added cancel execution handling
• Ensured safe termination of running agents

Testing

• Tested locally with multiple execution scenarios
• Verified no unintended side effects

Screenshots

Add screenshots to demonstrate UI changes.

[bryanadenhq]

Nitpick: Please change the name from Stop to Pause to make sure that the naming convention is correct.

Other than this, it looks good!

[Antiarin]

UI suggestion: dual-purpose send/stop button
Instead of a separate always-visible stop button, what about making it a send/stop toggle like ChatGPT and Claude's web UI do?

• No text in input → button disabled
• Text in input → shows "Send" / arrow icon, clicks to submit
• Execution running → switches to "Stop" / square icon, clicks to pause
• Matches the height of the input field, vertically centered

[ishaannk]

Hi reviewers, I’ve addressed the requested changes and updated the implementation accordingly. Please take another look and let me know if any further modifications are needed. Thank you!

[ishaannk]

Video.Pr.mp4

Will Improve UX! if needed