Adds two find_draggable_at tests covering the reported stock/waste
drag bug: clicking the visible top of a multi-card waste must pick the
top index (not the buffer card beneath), and a lone waste card must
still be draggable. Both pass against current logic, pinning the
correct behaviour.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
funman300