Game rules engine

Makes every game's rules a pure, deterministic TypeScript engine behind one game contract: the same seed and moves give the same states on iOS, Android, Jest and Node, so bots, solvers, saves, undo, replays and the daily level can all trust it. The skill ships the kit (src/core/game/: the contract types, the difficulty scale and the test helpers), a complete template game (the public-domain puzzle Lights Out) and a checker that proves the kit, the seeded RNG against its golden values and each game's rules, by running them.

Rules that must hold