supertensor: shape-aware tensor figure toolkit

Extracted from the tensor-formula-viz skill and rebuilt around the idea that
the geometry rules should be enforced by construction rather than restated as
prose an agent has to remember.

- assets/supertensor.sty: faces, stacks, index faces, shared caption lanes,
  meaning box, signature. Macros take a declared axis and a declared role, so
  equal shapes get equal edges, a x a is square, a transpose swaps the face,
  and contracted axes share an edge length -- without any manual alignment.
- scripts/preflight.sh: decide the TikZ/CJK path before drawing.
- scripts/build.sh: compile and fail on silent corruption (missing CJK glyphs,
  overfull boxes, undeclared roles), then export pdf/svg/png/thumb.
- scripts/test.sh: build every figure as a regression test for the package.
- examples/: three golden figures (TP-FFN, causal MHA, MoE top-k gather) plus
  an anti-pattern gallery of figures that compile cleanly and still lie.
- SKILL.md + references/: lean entry point, details loaded on demand.

tests/smoke.tex

@@ -0,0 +1,37 @@
+\documentclass[border=8pt]{standalone}
+\usepackage[cjk]{supertensor}
+
+\stsetrole{x}{stTeal}
+\stsetrole{w}{stOrange}
+\stsetrole{h}{stViolet}
+
+\stdim{m}{6}
+\stdim{k}{4}
+\stdim{n}{5}
+
+\begin{document}
+\begin{tikzpicture}
+  \stface[role=x, pattern=dense, bracket=true]{X}{(0,0)}{m}{k}
+  \stcaption{X}{$\mathbf X$}{$m\times k$}
+
+  \node[st op, right=4mm of X] (mul) {$\times$};
+
+  \stface[role=w, pattern=dense, bracket=true]{W}{($(mul)+(1.6,0)$)}{k}{n}
+  \stcaption{W}{$\mathbf W$}{$k\times n$}
+
+  \node[st op, right=4mm of W] (eq) {$=$};
+
+  \stface[role=h, pattern=dense, bracket=true]{H}{($(eq)+(1.8,0)$)}{m}{n}
+  \stcaption{H}{$\mathbf H$}{$m\times n$}
+
+  \ststack[role=x, pattern=causal]{S}{($(H)+(3.4,0)$)}{k}{k}{3}
+  \stcaption{S}{$\mathbf S$}{$b\times k\times k$}
+
+  \node[inner sep=0pt, fit=(X)(S)(H-shape)] (all) {};
+  \stmeaningbox{mb}{13cm}{all}
+    {$m$ 行、$k$ 收缩维、$n$ 输出维}
+    {$\mathbf X$ 激活值，$\mathbf W$ 权重，$\mathbf S$ 因果分数}
+    {$(m\times k)(k\times n)\rightarrow(m\times n)$}
+  \stsignature{Smoke test}{mb}
+\end{tikzpicture}
+\end{document}