feat(course): audit fixes and twelve extensions (Modules 7b, 12, 13)

Audit pass:
- Frame rule counts frames since the last move, so every step lasts
  exactly movesEvery(score) frames, also right after a speed-up
- clampTime + MAX_GAP_MS: a hidden tab no longer replays the whole gap
- Pong Restart keeps held keys
- Fact corrections (mulberry32 output coverage, Haskell IO, uniform)
- New fixture cases from a mutation analysis

Extensions (all three tracks, shared fixtures, course text):
- Turn queue (Exercise 10.6), persisted high score (10.7),
  replay viewer (10.8), play() end-to-end helper (9.5)
- Optional State (4.7) and optional Module 7b, stack-safe IO
- Module 12, property-based testing with generators, shrinking,
  invariants and a model-based oracle
- Module 13, Conway's Life with a Click event
- JS type checking via jsconfig, JSDoc and types.d.ts
- Maintainer tools: scripts/mutate.mjs, scripts/typecheck-js.sh,
  Playwright end-to-end suite (e2e/, scripts/e2e.sh)

Docs: docs/contract.md is the canonical contract; specs and build log
under docs/superpowers.

Verified: JS 728, Scala 689, F# 691 unit tests; stubs and progression
M01-M13 and M07b; 176 end-to-end tests on Chromium and WebKit.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

js/solutions/spawn.js

@@ -3,14 +3,17 @@ import { range, contains } from './util.js'
 import { point, pointEquals, initialState } from './model.js'
 import { advance } from './rules.js'
 import { intBelow, run } from './random.js'
+/** @import { Point, GameState } from './types' */
 
-/** Every board cell not covered by the snake, row-major (y outer, x inner). */
+/** Every board cell not covered by the snake, row-major (y outer, x inner).
+ * @type {(state: {width: number, height: number, snake: Point[]}) => Point[]} */
 export const freeCells = (state) =>
   range(state.height)
     .flatMap((y) => range(state.width).map((x) => point(x, y)))
     .filter((p) => !contains(state.snake, p, pointEquals))
 
-/** Put an apple on a random free cell; a full board means the player has won. */
+/** Put an apple on a random free cell; a full board means the player has won.
+ * @type {(state: GameState) => GameState} */
 export const spawnApple = (state) => {
   if (state.apple !== null || state.status !== 'Playing') return state
   const cells = freeCells(state)
@@ -19,8 +22,10 @@ export const spawnApple = (state) => {
   return { ...state, apple: cells[i], seed }
 }
 
-/** One game step: move the snake, then make sure there is an apple. */
+/** One game step: move the snake, then make sure there is an apple.
+ * @type {(state: GameState) => GameState} */
 export const tick = (state) => spawnApple(advance(state))
 
-/** A fresh game with its first apple already placed. */
+/** A fresh game with its first apple already placed.
+ * @type {(seed: number) => GameState} */
 export const newGame = (seed) => spawnApple(initialState(seed))