WIP: pre-existing changes from WASM browser work + test infrastructure

Accumulated changes from WASM browser development sessions:
- sx_runtime.ml: signal subscription + notify, env unwrap tolerance
- sx_browser.bc.js: rebuilt js_of_ocaml browser kernel
- sx_browser.bc.wasm.js + assets: WASM browser kernel build
- sx-platform.js browser tests (test_js, test_platform, test_wasm)
- Playwright sx-inspect.js: interactive page inspector tool
- harness-web.sx: DOM assertion updates
- deploy.sh, Dockerfile, dune-project: build config updates
- test-stepper.sx: stepper unit tests
- reader-macro-demo plan update

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy.sh

@@ -63,8 +63,12 @@ for app in "${BUILD[@]}"; do
   echo "=== $app ==="
   docker build -f "$dir/Dockerfile" -t "$REGISTRY/$app:latest" .
   docker push "$REGISTRY/$app:latest"
-  docker service update --force "coop_$app" 2>/dev/null \
-    || echo "  (service coop_$app not running — will start on next stack deploy)"
+  case "$app" in
+    sx_docs) svc="sx-web_sx_docs" ;;
+    *)       svc="coop_$app" ;;
+  esac
+  docker service update --force "$svc" 2>/dev/null \
+    || echo "  (service $svc not running — will start on next stack deploy)"
   echo ""
 done