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>

fsharp/solutions/Model.fs

@@ -25,6 +25,7 @@ type Action =
     | Frame
 
 /// The whole game. `Snake` is head first; `Seed` is the unsigned 32-bit random seed.
+/// `Frame` and `Queued` stay unused until m10 (`Queued` holds a turn waiting for the next step).
 type GameState =
     { Width: int
       Height: int
@@ -35,7 +36,8 @@ type GameState =
       Seed: uint32
       Score: int
       Status: Status
-      Frame: int }
+      Frame: int
+      Queued: Direction option }
 
 let delta (dir: Direction) : Point =
     match dir with
@@ -61,4 +63,5 @@ let initialState (seed: uint32) : GameState =
       Seed = seed
       Score = 0
       Status = Playing
-      Frame = 0 }
+      Frame = 0
+      Queued = None }