feat(js): m04 random and spawn with fixtures and tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

js/src/spawn.js

@@ -0,0 +1,17 @@
+import { todo } from './todo.js'
+
+/** Every board cell not covered by the snake, row-major (y outer loop, x inner loop). The apple does not count as occupied. */
+export const freeCells = (state) => todo('m04')
+
+/**
+ * Put an apple on a random free cell, drawing from `state.seed` (use `intBelow` and store the new seed).
+ * Unchanged if there already is an apple or the status is not 'Playing'.
+ * If no cell is free the board is full: status becomes 'Won' (seed unchanged, no apple).
+ */
+export const spawnApple = (state) => todo('m04')
+
+/** One game step: `advance`, then make sure there is an apple. */
+export const tick = (state) => todo('m04')
+
+/** A fresh game (`initialState`) with its first apple already placed. */
+export const newGame = (seed) => todo('m04')