feat: add superderive stepwise derivation figures

A third sibling toolkit: rewrite steps, justification rails,
cancel/substitute highlights, and lint-on-warning builds.

scripts/test.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+set -uo pipefail
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+fail=0
+for f in "$ROOT"/tests/*.tex "$ROOT"/examples/*.tex; do
+  [[ -e "$f" ]] || continue
+  name="$(basename "$f")"
+  if "$ROOT/scripts/build.sh" "$f" >/dev/null 2>&1; then
+    echo "  ok    $name"
+  else
+    echo "  FAIL  $name"
+    fail=$((fail+1))
+  fi
+done
+for f in "$ROOT"/tests/lint-invalid/*.tex; do
+  [[ -e "$f" ]] || continue
+  name="$(basename "$f")"
+  if python3 "$ROOT/scripts/lint.py" "$f" >/dev/null 2>&1; then
+    echo "  FAIL  $name (invalid fixture passed lint)"
+    fail=$((fail+1))
+  else
+    echo "  ok    $name (rejected by lint)"
+  fi
+done
+if [[ $fail -gt 0 ]]; then
+  echo "$fail failing check(s)" >&2
+  exit 1
+fi
+echo "all superderive checks passed"