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>

scripts/typecheck-js.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# Usage: scripts/typecheck-js.sh
+# Type-checks the JavaScript track with TypeScript, using js/jsconfig.json and the types in js/src/types.d.ts.
+# Two runs, both must be clean:
+#   1. the untouched stubs in js/src (a student's starting point must not show errors in the editor);
+#   2. a temp copy of the repo whose js/src holds the solutions.
+# Nothing is installed in the repo: TypeScript comes from `npx -y -p typescript tsc`, which needs the network the
+# first time (npm caches it afterwards). Set TS_PACKAGE to pin a version, e.g. TS_PACKAGE=typescript@5.9.
+# Exit: 0 clean, 1 type errors, 2 TypeScript could not be run (no npx, no network).
+set -uo pipefail
+repo="$(cd "$(dirname "$0")/.." && pwd)"
+pkg="${TS_PACKAGE:-typescript}"
+
+if ! command -v npx >/dev/null 2>&1; then
+  echo "typecheck-js: npx not found (it comes with Node.js); cannot run TypeScript" >&2; exit 2
+fi
+if ! version="$(npx -y -p "$pkg" tsc --version 2>&1)"; then
+  echo "typecheck-js: could not run 'npx -y -p $pkg tsc' (no network, or npm cannot reach its registry)." >&2
+  echo "$version" | tail -5 >&2
+  echo "typecheck-js: nothing was checked." >&2
+  exit 2
+fi
+version="$(grep -o 'Version .*' <<<"$version")"
+
+tmp="$(mktemp -d)"
+trap 'rm -rf "$tmp"' EXIT
+tar -C "$repo" --exclude=.git --exclude=node_modules --exclude=bin --exclude=obj \
+    --exclude=.scala-build --exclude=.bsp --exclude=.superpowers -cf - js | tar -C "$tmp" -xf -
+mkdir -p "$tmp/stubs" "$tmp/solved"
+cp -r "$tmp/js" "$tmp/stubs/js"
+mv "$tmp/js" "$tmp/solved/js"
+rm -rf "$tmp/solved/js/src"
+cp -r "$tmp/solved/js/solutions" "$tmp/solved/js/src"
+
+status=0
+for which in stubs solved; do
+  label="$([ "$which" = stubs ] && echo "js/src (stubs)" || echo "js/solutions as src")"
+  if out="$(cd "$tmp/$which" && npx -y -p "$pkg" tsc -p js/jsconfig.json 2>&1)"; then
+    echo "$label: ok ($version)"
+  else
+    echo "$label: FAIL"
+    grep -v '^npm notice' <<<"$out"
+    status=1
+  fi
+done
+exit $status