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

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

scala/solutions/Spawn.scala

@@ -0,0 +1,25 @@
+package snake
+
+/** m04 spawn: placing apples with the Random from Random.scala. */
+object Spawn:
+
+  def freeCells(state: GameState): List[Point] =
+    for
+      y <- Util.range(state.height)
+      x <- Util.range(state.width)
+      p = Point(x, y)
+      if !Util.contains(state.snake, p, _ == _)
+    yield p
+
+  def spawnApple(state: GameState): GameState =
+    if state.apple.isDefined || state.status != Status.Playing then state
+    else
+      val cells = freeCells(state)
+      if cells.isEmpty then state.copy(status = Status.Won)
+      else
+        val (i, seed) = Random.intBelow(cells.length).run(state.seed)
+        state.copy(apple = Some(cells(i)), seed = seed)
+
+  def tick(state: GameState): GameState = spawnApple(Rules.advance(state))
+
+  def newGame(seed: Long): GameState = spawnApple(Model.initialState(seed))