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/pong/rules.js

@@ -1,7 +1,9 @@
 // m11 pong rules: one pure `pongUpdate`, built from small steps that each return a new piece of state.
 import { H, W, PADDLE, PLAYER_X, CPU_X, WIN, initialPong } from './model.js'
 import { nextUint32 } from '../random.js'
+/** @import { PongState, PongAction } from '../types' */
 
+/** @type {(lo: number, hi: number, x: number) => number} */
 export const clamp = (lo, hi, x) => Math.min(hi, Math.max(lo, x))
 
 const clampPaddle = (y) => clamp(0, H - PADDLE, y)
@@ -62,11 +64,13 @@ const heldFlag = { Up: 'up', Down: 'down' }
 const setHeld = (state, key, value) =>
   Object.hasOwn(heldFlag, key) ? { ...state, held: { ...state.held, [heldFlag[key]]: value } } : state
 
+/** @type {(state: PongState, action: PongAction) => PongState} */
 export const pongUpdate = (state, action) => {
   switch (action.tag) {
     case 'Press': return setHeld(state, action.key, true)
     case 'Release': return setHeld(state, action.key, false)
-    case 'Restart': return initialPong(state.seed)
+    // A new match, but the keys are still where the player's fingers are.
+    case 'Restart': return { ...initialPong(state.seed), held: state.held }
     case 'Frame': return frame(state)
     default: return state
   }