has_legal_moves: was only checking the top face-up card of each tableau
column as a move source. In Klondike any face-up card can anchor a
movable run, so mid-column cards were missed, causing premature game-over
declarations. Now iterates all face-up cards in each column.
Also tightened the source set: stock (face-down) cards were included
as placement sources producing false positives; waste now only considers
its top card (the one actually reachable by the player).
Waste flash: card_positions rendered exactly `visible` waste cards, so
the card sliding off-pile was despawned the same frame the draw tween
started, causing a one-frame flash. Now renders `visible + 1` cards;
the extra card sits at x=0 (hidden under the stack) and disappears
naturally once the tween positions the new top card over it.
Adds regression test: non-top face-up tableau card as only legal move.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
funman300
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