violation check changes, welcome popup, game end button, better looking header, better refiner prompting

[PaulScotti]

• Better looking top header
• Welcome pop-up to explain how the game works
• Placeholder End Game button that switches to a placeholder multiple choice to select the murderer
• Slightly improved prompting for refiner
• Now using "Principles" approach for violation checking, see changes to critique prompting and characters.json
• Explicitly added clues to each suspect's context that contains "hidden" information about the other suspects. Idea is that you we want each suspect's secret about themselves to never be revealed, but they should be able to reveal hints to other suspects' secrets (otherwise this game will be impossible to beat if we assume that our violation checker works perfectly)
• Now "Detective Sheerluck:" gets prepended to every user response to help the AI make sense of who's saying what in the chat log