feat(scala): m01–m06 port with shared fixtures

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scala/solutions/Game.scala

@@ -0,0 +1,14 @@
+package snake
+
+/** m05 game: one `update` turns every action into a new state; replaying a game is a fold over its actions. */
+object Game:
+
+  def update(state: GameState, action: Action): GameState = action match
+    case Action.Tick       => Spawn.tick(state)
+    case Action.Turn(dir)  => Rules.turn(state, dir)
+    case _                 => state // TogglePause, Restart and Frame arrive in m10
+
+  def replay(state: GameState, actions: List[Action]): GameState = actions.foldLeft(state)(update)
+
+  // scanLeft is foldLeft that keeps every intermediate result.
+  def history(state: GameState, actions: List[Action]): List[GameState] = actions.scanLeft(state)(update)