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.

references/antipatterns.md

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+# Anti-patterns
+
+Each of these can compile cleanly and still teach the reader something false.
+Rendered pairs: `examples/antipatterns.tex`.
+
+- **A decorative arrow.** The arrow has no data/control/dependency meaning. Remove it or
+  make the relationship explicit.
+- **A group that is only a visual border.** The outline does not correspond to a real
+  module/composite in the paper.
+- **One node doing two jobs.** "attention + layer norm + residual" in one block hides the
+  mechanism the figure was meant to explain.
+- **A new hue for a slightly different view of the same object.** Reuse the role or use
+  lightness, not a fresh color family.
+- **A caption repeated in the meaning box.** Captions name the objects; the meaning box
+  explains what they do and why.
+- **Solving crowding by shrinking type.** The type hierarchy is a hard floor. Move the
+  stage to another row or split the figure.
+- **Magic offsets.** Every hand-tuned coordinate is valid only for the current label. The
+  next edit will land a longer label on a neighbor.
+- **A floating commentary card between objects.** If it is not an object or edge, it belongs
+  in the stage subtitle, meaning box, or one `\sfcallout` beside a finished band.