Give every sin a pictogram for navigation

The gallery and the cross-links were all text, so nothing on either told
you what the chart problem actually looked like.

Shrinking the bad chart doesn't work here: in nearly every sin the tell
lives in the axis, the scale or the legend, which is exactly what a chart
loses at thumbnail size. Eight miniatures would have been eight
indistinguishable squiggles with the evidence stripped out.

So each sin gets a hand-drawn glyph of the tell instead — a cut baseline,
a down-pointing axis arrow, class breaks that moved between two ramps.
Banner across the top of the gallery tile, small glyph beside each
"Often found together" link. Drawn against currentColor plus three theme
tokens, so unlike the baked chart SVGs these follow light and dark.

Missing thumbnail throws at build, same as an unknown citation key.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ULE5RRxdQE1ebwefEd2eCM

src/thumbs/incomplete-pie.svg

@@ -0,0 +1,7 @@
+<!-- Three quarters of a result, with the fourth simply absent. -->
+<svg viewBox="0 0 72 48" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <path d="M36 24h17A17 17 0 1 1 36 7z" fill="currentColor" opacity=".14" />
+  <path d="M53 24A17 17 0 1 1 36 7" stroke="currentColor" stroke-width="2" />
+  <path d="M36 24v17M36 24H19" stroke="currentColor" stroke-width="2" />
+  <path d="M36 24h17M36 24V7" stroke="var(--thumb-accent)" stroke-width="2" />
+</svg>