Add CargoFilter property to PieceState, auto-assigned at placement
by tracing relay chain back to production. TransferResolver now
enforces cargo-type filtering and uses forward-direction sorting
with cargo-aware distance calculations. Prevents cross-route
contamination on multi-cargo boards.
Level 3 restored to dual-cargo (Wood+Stone) with correct 10R+2K stock.
Two new solvability tests validate filter auto-assignment and chain
propagation. All 60 tests green.
Black box sim engine (commands in, events out) with 3 piece types
(Rook, Bishop, Knight), cargo transfer system with social status
priority, collision detection, and victory/defeat conditions.
57 tests covering rules, simulation, loading, and solvability.
Godot 4 presentation layer scaffolding.
