- Add GameSetup component with Duolingo-style button selectors for
language pair, POS, difficulty, and rounds
- Language swap: selecting the same language for source and target
automatically swaps them instead of allowing duplicates
- Add selection-before-submission flow: user clicks an option to
highlight it, then confirms with a Submit button to prevent misclicks
- Add selected state to OptionButton (purple ring highlight)
- Play Again on score screen returns to settings instead of
auto-restarting with the same configuration
- Remove hardcoded GAME_SETTINGS, game configuration is now user-driven
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