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/solutions/Model.scala

@@ -17,7 +17,10 @@ enum Action:
   case Restart
   case Frame
 
-/** The whole game. `snake` is head first; `seed` is the unsigned 32-bit random seed (0 until 2^32). */
+/**
+ * The whole game. `snake` is head first; `seed` is the unsigned 32-bit random seed (0 until 2^32).
+ * `frame` and `queued` stay unused until Module 10 (`queued` is the turn waiting for the next step, Exercise 10.6).
+ */
 final case class GameState(
     width: Int,
     height: Int,
@@ -28,7 +31,8 @@ final case class GameState(
     seed: Long,
     score: Int,
     status: Status,
-    frame: Int
+    frame: Int,
+    queued: Option[Direction]
 )
 
 /** m02 model: the data the whole game is built from. Case classes and enums are immutable. */
@@ -56,5 +60,6 @@ object Model:
     seed = seed,
     score = 0,
     status = Status.Playing,
-    frame = 0
+    frame = 0,
+    queued = None
   )