- Add Rank=1..13 explicit discriminants so `rank as u8 == rank.value()`; collapse 13-arm value() match to `self as u8`
- Add Rank::RANKS and Suit::SUITS iteration constants
- Add Rank::checked_add / checked_sub (const fn, type-safe boundary enforcement); update rules.rs to use them
- Add GameState::possible_instructions() enumerating all valid move_cards triples (foundation for hints/solver)
- Fix waste buffer card peeking through during draw-slide animation by setting Visibility::Hidden on the buffer entity in sync_cards
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
funman300
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