Add inverted-axis and aspect-ratio sins; rename slugs

Writes two sins off the backlog. The inverted y-axis is the egregious
one: the fill hangs from the top and the line descends while the values
climb, with every element individually defensible. Aspect ratio is the
quiet one: same twelve numbers, same y-range, only the shape of the box
changes.

Adds Cleveland, McGill & McGill 1988 to the canon — banking to 45 comes
from the shape-parameter paper, not the 1984 ranking already cited, so
citing the latter for it would have misattributed the claim.

Also renames sin slugs to match their retitled pages, and rewrites the
summaries that had started echoing those titles.

Gives line-chart points their mark color explicitly; "point": true was
falling back to Vega's default blue on a red or green line.

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

src/content/sins/aspect-ratio.md

@@ -0,0 +1,53 @@
+---
+title: "Aspect Ratio That Exaggerates a Trend"
+summary: "Drawn tall and narrow it's a cliff; drawn wide it's a shrug. Same series, both times."
+poke: "You didn't change a number — you changed the shape of the box, and the trend changed with it."
+category: "Misleading Scales"
+severity: 3
+tags: ["line chart", "aspect ratio", "exaggeration"]
+badChart: "aspect-ratio-bad"
+fixedChart: "aspect-ratio-fixed"
+date: 2026-08-05
+citations:
+  - key: shapeparameter
+    note: "The paper that made this measurable: a graph's width-to-height ratio changes how slopes are judged, and gave us “bank the average slope toward 45°.”"
+  - key: clevelandmcgill
+    note: "Slope is one of the elementary perceptual tasks they ranked — and it's the one the shape of the box distorts."
+  - key: howchartslie
+    note: "Cairo on proportions as a storytelling lever, not a neutral container."
+---
+
+## The sin
+
+Two panels, twelve identical numbers, one identical y-range of 170–280 ms. The
+only difference is the shape of the plotting area: one is tall and narrow, one
+is a conventional landscape rectangle.
+
+The narrow panel reads like an emergency. The wide one reads like a system
+drifting slowly and predictably. Both are the same 47% rise.
+
+## Why it deceives
+
+The eye judges a trend by the **angle** of the line, and angle is a product of
+the data *and* the box you draw it in. Squeeze the width and every segment tilts
+toward vertical; stretch it and everything flattens toward nothing. Cleveland
+and colleagues named this the graph's *shape parameter* and showed the effect is
+real and measurable, not a matter of taste.
+
+What makes this one slippery is that the sinner usually isn't sinning. Nobody
+sets out to pick a dishonest aspect ratio — they drop a chart into the space a
+slide template left them, or a dashboard tile stretches it to fill a column.
+The distortion arrives by default, which is exactly why it survives review: the
+numbers are right, the axis is right, and there is nothing to point at.
+
+## The repentance
+
+Treat the ratio as an encoding decision, because that's what it is. The classic
+guidance is to shape the plot so the average slope of the line sits somewhere
+near 45° — steep enough to read, shallow enough not to shout. Neither extreme
+above qualifies; the wide panel is the more honest of the two, and it could
+stand to be a little taller still.
+
+Then hold the shape **constant across charts you want compared**. A dashboard
+where each tile stretches to fill its slot has silently given every series a
+different exaggeration factor, and no reader will know which trends are real.