feat: Add a "Start over" button left of the "Reset" button on the header with functionality

[spenceriam]

Add a button "Start over" which mimics the button used at the workflow complete screen. When this button is pressed to take the user back to the describe your feature screen. Add a check, if the user is already on that screen or is on the API key validation or AI model selection screens to check if both are complete else grey the button out. Have a confirmation modal - if Yes then proceed, if no - close modal.