Add SDL-free Board model: Board.h, Board.cpp
Add unit tests for Board using Google Test: test_board.cpp
Integrate test_board into CMake and register with CTest: update CMakeLists.txt
Add gtest to vcpkg.json so CMake can find GTest
Add high-level refactor plan: plan-spacetrisRefactor.prompt.md
Update internal TODOs to mark logic extraction complete
This scaffolds deterministic, testable game logic and CI-friendly tests without changing existing runtime behavior.
- Added a pure, SDL-free Board model implementing grid access and clearFullLines().
- Added a small standalone test at test_board.cpp (simple assert-based; not yet wired into CMake).
