fix(website): prefix astrochart.js path with BASE_URL (#112)

* CI: fix docs-deploy Node version for Astro build

The deploy workflow ran the library build (webpack, Node 20) and the
Astro website build in the same job under node-version 20, causing
Astro to fail with "Node.js v20 is not supported".

A single job can only run one Node version, so split the build job:

- build-library (Node 20): builds the webpack bundle and uploads it
  as a GitHub Actions artifact
- build-website (Node 22): downloads the bundle, copies it into
  website/public/, installs website deps, builds the Astro site, and
  uploads the Pages artifact
- deploy: now depends on build-website (unchanged otherwise)

🤖 Generated with [eca](https://eca.dev)

Co-Authored-By: eca <git@eca.dev>

* fix(website): prefix astrochart.js path with BASE_URL

The bundle was hard-coded as '/astrochart.js' (root-relative) in
ChartDemo.astro. With base: '/AstroChart' in astro.config.mjs the
file is deployed at /AstroChart/astrochart.js, so the browser was
requesting the wrong path and getting a 404.

Pass import.meta.env.BASE_URL into the is:inline script via
define:vars and prefix both the querySelector guard and the dynamic
script.src with it. Astro guarantees BASE_URL ends with '/', so
concatenating 'astrochart.js' produces the correct path.

🤖 Generated with [eca](https://eca.dev)

Co-Authored-By: eca <git@eca.dev>

---------

Co-authored-by: eca <git@eca.dev>

Author: afucher

website/src/components/ChartDemo.astro

@@ -78,7 +78,8 @@ const codeSnippet = getCodeSnippet()
     chartMode: mode,
     chartHeight: height,
     radixData: defaultRadixData,
-    transitData: defaultTransitData
+    transitData: defaultTransitData,
+    baseUrl: import.meta.env.BASE_URL
   }}
 >
   ;(function () {
@@ -112,7 +113,7 @@ const codeSnippet = getCodeSnippet()
     if (window.astrochart) {
       // Library already loaded — init immediately
       initChart()
-    } else if (document.querySelector('script[src="/astrochart.js"]')) {
+    } else if (document.querySelector('script[src="' + baseUrl + 'astrochart.js"]')) {
       // Another instance is already loading the bundle — queue up
       window.__astrochartQueue = window.__astrochartQueue || []
       window.__astrochartQueue.push(initChart)
@@ -122,7 +123,7 @@ const codeSnippet = getCodeSnippet()
       window.__astrochartQueue.push(initChart)
 
       var script = document.createElement('script')
-      script.src = '/astrochart.js'
+      script.src = baseUrl + 'astrochart.js'
       script.onload = function () {
         var queue = window.__astrochartQueue || []
         window.__astrochartQueue = []