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/web/ReplayMain.fs

@@ -0,0 +1,39 @@
+/// fsharp/replay.html loads this module (web/dist/ReplayMain.js): the replay viewer of m10.
+/// The recording is plain JSON next to the test fixtures; the page is served from the repository root by
+/// scripts/serve.mjs, so it can be fetched (relative to the page, fsharp/replay.html). It is decoded with plain
+/// JavaScript interop, without a JSON library, and the viewer starts once it has arrived.
+module Snake.Web.ReplayMain
+
+open Fable.Core
+open Fable.Core.JsInterop
+open Snake
+open Snake.Model
+open Snake.Replay
+
+[<Global>]
+let private window: obj = jsNative
+
+let private direction (dir: string) : Direction =
+    match dir with
+    | "Up" -> Up
+    | "Down" -> Down
+    | "Left" -> Left
+    | "Right" -> Right
+    | other -> failwith $"unknown direction in the recording: {other}"
+
+// A recording holds only Tick and Turn: {"tag":"Tick"} or {"tag":"Turn","dir":"Up"}.
+let private action (a: obj) : Action =
+    match (a?tag: string) with
+    | "Tick" -> Tick
+    | "Turn" -> Turn(direction a?dir)
+    | other -> failwith $"unknown action in the recording: {other}"
+
+let private recording (data: obj) : Recording =
+    { Seed = uint32 (data?seed: float)
+      Actions = (data?actions: obj[]) |> Array.map action |> List.ofArray }
+
+let private start (data: obj) : unit =
+    Runtime.runApp (BrowserPlatform.create (BrowserPlatform.gameCanvas ())) (replayMain (recording data))
+
+window?fetch("../fixtures/replay-sample.json")?``then``(fun (response: obj) -> response?json ())?``then``(start)
+|> ignore