Add favicon, clear button, and other improvements

[simran-kaur5]

This pull request enhances the Password Generator project with the following improvements:

• Added a favicon.
• Added a Clear Password button to quickly reset the password field.
• Updated clipboard button to show a temporary white tick when password is copied.
• Minor UI/UX improvements for better user interaction.
• Optimized JavaScript for easier maintenance.

These changes improve usability and give users visual feedback on password strength and actions.