Scaffold Chart Sins site with Astro + build-time Vega-Lite

Set up the static-site tech stack: Astro 5 with Markdown content
collections, Vega-Lite specs rendered to static SVG at build time
(zero client JS), plain scoped CSS, and a GitHub Pages deploy workflow.

Includes three sample sins (truncated y-axis, dual-axis deception,
pie chart overload), each with a bad and fixed chart spec, plus a
gallery index and per-sin detail pages.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XPEvmMbac2fCvKXpQcovj8

src/content/sins/dual-axis-deception.md

@@ -0,0 +1,30 @@
+---
+title: "The Dual-Axis Deception"
+summary: "Two unrelated series on two independent axes, engineered to look correlated."
+category: "False Relationships"
+severity: 5
+tags: ["dual axis", "correlation", "line chart"]
+badChart: "dual-axis-bad"
+fixedChart: "dual-axis-fixed"
+date: 2026-08-05
+---
+
+## The sin
+
+Put two series on the same plot with two independent y-axes and you can make
+*anything* look correlated. Slide the scales until the lines overlap and the
+reader's brain does the rest: "these move together, so one must cause the other."
+
+## Why it deceives
+
+With independent axes, the vertical position of each line is arbitrary — you
+chose it. Overlapping lines imply a relationship that exists only because you
+tuned two scales to coincide. Ice cream sales and shark attacks both rise in
+summer; neither causes the other. The shared season is the hidden variable.
+
+## The repentance
+
+Don't force two series into one coordinate space just to imply a link. Show them
+in **separate, stacked panels** with honest zero-based scales. If you truly want
+to argue they move together, plot one **against** the other (a scatter plot) and
+let the reader judge the relationship — don't manufacture it with axis scaling.