feat: add superfig paper-figure toolkit

Standalone LaTeX/TikZ skill for non-tensor paper figures: node/edge
macros, lint-on-warning build, golden examples, and negative fixtures.

tests/group-callout.tex

@@ -0,0 +1,32 @@
+% Group expands the last row so captions clear the outline.
+% One callout hangs off the finished band.
+\documentclass[border=8pt]{standalone}
+\usepackage[en]{superfig}
+
+\sfsetrole{q}{sfTeal}
+\sfsetrole{w}{sfOrange}
+
+\begin{document}
+\begin{tikzpicture}
+\sfstage{S}{composite plus aside}
+\sfrow{R1}{12mm}
+  \sfnode[role=q]{A}{$A$}{14mm}{10mm}
+  \sfconn{e1}{}
+  \sfnode[role=q]{B}{$B$}{14mm}{10mm}
+  \sfgap{\sflinklen}
+  \sfnode[role=w]{C}{$C$}{14mm}{10mm}
+\sfrowend
+\sfgroup[role=q]{G}{(A)(B)}{}
+\sfarrow{G.east}{C.west}
+\sflane{R1}
+\sfcaption{G}{$AB$}{one composite}
+\sfcaption{C}{$C$}{consumer}
+\sfcallout{N1}{32mm}{R1}{aside}{The card hangs off the band, not off $C$.}
+\sfbbox{all}
+\sftopformula{F}{$C = f(AB)$}
+\sfmeaningbox{mb}{108mm}{all}
+  {a group is a real composite}
+  {pair $AB$, consumer $C$}
+  {captions sit below the outline because the group refits the row}
+\end{tikzpicture}
+\end{document}