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>

scala/test/Fixtures.test.scala

@@ -40,9 +40,20 @@ object Fixtures:
     seed = v("seed").num.toLong,
     score = v("score").num.toInt,
     status = status(v("status")),
-    frame = v("frame").num.toInt
+    frame = v("frame").num.toInt,
+    queued = opt(v("queued"))(direction)
   )
 
+  def session(v: ujson.Value): Session =
+    Session(gameState(v("game")), v("best").num.toInt, v("improved").bool)
+
+  def event(v: ujson.Value): Event = v("tag").str match
+    case "Time"    => Event.Time(v("t").num.toLong)
+    case "KeyDown" => Event.KeyDown(v("key").str)
+    case "KeyUp"   => Event.KeyUp(v("key").str)
+    case "Click"   => Event.Click(v("x").num.toInt, v("y").num.toInt)
+    case other     => throw new IllegalArgumentException(s"unknown event tag: $other")
+
   def shape(v: ujson.Value): Shape = v("tag").str match
     case "Rect" => Shape.Rect(v("x").num.toInt, v("y").num.toInt, v("w").num.toInt, v("h").num.toInt, v("color").str)
     case "Text" =>