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>

fixtures/m10-viewer-update.json

@@ -0,0 +1,23 @@
+{
+  "function": "viewerUpdate",
+  "cases": [
+    {"name":"next-moves-one-frame-forward","args":[{"index":3,"last":10,"playing":false},{"tag":"Next"}],"expected":{"index":4,"last":10,"playing":false}},
+    {"name":"next-at-the-last-frame-stays","args":[{"index":10,"last":10,"playing":false},{"tag":"Next"}],"expected":{"index":10,"last":10,"playing":false}},
+    {"name":"prev-moves-one-frame-back","args":[{"index":3,"last":10,"playing":false},{"tag":"Prev"}],"expected":{"index":2,"last":10,"playing":false}},
+    {"name":"prev-at-the-first-frame-stays","args":[{"index":0,"last":10,"playing":false},{"tag":"Prev"}],"expected":{"index":0,"last":10,"playing":false}},
+    {"name":"first-goes-to-frame-zero","args":[{"index":7,"last":10,"playing":false},{"tag":"First"}],"expected":{"index":0,"last":10,"playing":false}},
+    {"name":"last-goes-to-the-last-frame","args":[{"index":2,"last":10,"playing":false},{"tag":"Last"}],"expected":{"index":10,"last":10,"playing":false}},
+    {"name":"toggle-play-starts-autoplay","args":[{"index":4,"last":10,"playing":false},{"tag":"TogglePlay"}],"expected":{"index":4,"last":10,"playing":true}},
+    {"name":"toggle-play-stops-autoplay","args":[{"index":4,"last":10,"playing":true},{"tag":"TogglePlay"}],"expected":{"index":4,"last":10,"playing":false}},
+    {"name":"toggle-play-at-the-end-starts-again-from-the-first-frame","args":[{"index":10,"last":10,"playing":false},{"tag":"TogglePlay"}],"expected":{"index":0,"last":10,"playing":true}},
+    {"name":"beat-while-playing-moves-one-frame-forward","args":[{"index":4,"last":10,"playing":true},{"tag":"Beat"}],"expected":{"index":5,"last":10,"playing":true}},
+    {"name":"beat-while-not-playing-is-ignored","args":[{"index":4,"last":10,"playing":false},{"tag":"Beat"}],"expected":{"index":4,"last":10,"playing":false}},
+    {"name":"beat-that-reaches-the-last-frame-stops-autoplay","args":[{"index":9,"last":10,"playing":true},{"tag":"Beat"}],"expected":{"index":10,"last":10,"playing":false}},
+    {"name":"next-while-playing-keeps-playing","args":[{"index":4,"last":10,"playing":true},{"tag":"Next"}],"expected":{"index":5,"last":10,"playing":true}},
+    {"name":"prev-while-playing-keeps-playing","args":[{"index":4,"last":10,"playing":true},{"tag":"Prev"}],"expected":{"index":3,"last":10,"playing":true}},
+    {"name":"last-while-playing-stops-autoplay","args":[{"index":4,"last":10,"playing":true},{"tag":"Last"}],"expected":{"index":10,"last":10,"playing":false}},
+    {"name":"first-while-playing-keeps-playing","args":[{"index":4,"last":10,"playing":true},{"tag":"First"}],"expected":{"index":0,"last":10,"playing":true}},
+    {"name":"a-recording-with-no-actions-cannot-play","args":[{"index":0,"last":0,"playing":false},{"tag":"TogglePlay"}],"expected":{"index":0,"last":0,"playing":false}},
+    {"name":"a-recording-with-no-actions-stays-at-frame-zero","args":[{"index":0,"last":0,"playing":false},{"tag":"Next"}],"expected":{"index":0,"last":0,"playing":false}}
+  ]
+}