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

astro.config.mjs

@@ -0,0 +1,11 @@
+// @ts-check
+import { defineConfig } from 'astro/config';
+import mdx from '@astrojs/mdx';
+
+// This is a *project* GitHub Pages site, so it is served from a sub-path.
+// If you later use a custom domain, set `site` to it and drop `base`.
+export default defineConfig({
+  site: 'https://olehomelchenko.github.io',
+  base: '/chart-sins',
+  integrations: [mdx()],
+});