Write a complete C++ terminal Snake game in this workspace.

Requirements:
1. Single file `snake.cpp` (C++17 ok). Use POSIX terminal I/O: raw mode or ncurses; WASD or arrow keys; quit with `q`.
2. Features: moving snake, food, grow on eat, wall or self collision ends game, score printed, board roughly 20x20 or similar.
3. `Makefile` with target `snake` that runs `g++ -O2 -o snake snake.cpp` (link `-lncurses` only if you use ncurses).
4. After writing, run `make` to verify it compiles. Do not need an interactive play session.
5. Brief README.md with how to build and run.

Use write_file / run_shell tools. Prefer implementing yourself rather than downloading.