feat: add superderive stepwise derivation figures

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

scripts/preflight.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Exit 0 full, 1 degraded, 2 no LaTeX.
+set -uo pipefail
+QUIET=0
+[[ "${1:-}" == "--quiet" ]] && QUIET=1
+say() { [[ $QUIET -eq 1 ]] || echo -e "$*"; }
+ok=0; warn=0; fail=0
+check() {
+  local name="$1"; shift
+  if "$@" >/dev/null 2>&1; then say "  ok    $name"; return 0
+  else say "  MISS  $name"; return 1; fi
+}
+say "superderive preflight"
+say "--- required ---"
+check "xelatex"        command -v xelatex        || fail=$((fail+1))
+check "standalone.cls" kpsewhich standalone.cls  || fail=$((fail+1))
+check "tikz.sty"       kpsewhich tikz.sty        || fail=$((fail+1))
+check "etoolbox.sty"   kpsewhich etoolbox.sty    || fail=$((fail+1))
+say "--- chinese figures ---"
+check "ctex.sty" kpsewhich ctex.sty || warn=$((warn+1))
+check "fandol"   kpsewhich FandolSong-Regular.otf || warn=$((warn+1))
+say "--- export ---"
+check "pdftocairo" command -v pdftocairo || warn=$((warn+1))
+if [[ $fail -gt 0 ]]; then say "RESULT: no LaTeX."; exit 2; fi
+if [[ $warn -gt 0 ]]; then say "RESULT: degraded."; exit 1; fi
+say "RESULT: full path."
+exit 0