feat: implemented Ctrl+Enter keyboard shortcut for prompt textarea

[reory]

Description

Closes #8

This PR addressed the issue where the Ctrl+Enter shortcut was not firing while typing
inside the prompt text box.

Changes Implemented

• Updated frontend/app.js to target the prompt element directly instead of
  listening globally on the document.
• Added e.preventDefault() to stop the browser from inserting an unwanted new
  line inside the textbox area when the shortcut is used.
• Added descriptive comments for future maintainers.

Testing features

• Verified locally that Ctrl+Enter successfully triggers the evaluation.
• Verified that pressing Enter by itself still correctly creates a new line.

[reory]

hi @nive62tech
Just dropping a gentle note on this one. Its been a couple of weeks.
The PR cleanly fixes the Ctrl+Enter shortcut issue mentioned in #8 and there are no merge conflicts.
Whenever you have a spare moment to take a look please would be greatly appreciated.

Thank you for maintaining the project. 😊

[nive62tech]

Great work @reory !
Love that you targeted the textarea specifically and added preventDefault — that's a much cleaner implementation. Merging this in!
Thank you for contributing

[reory]

@nive62tech Thank you 😊