Fix anchor link handling in translations

Fixes an issue where anchor links (e.g., webgpu-fundamentals.html#section)
in translation pages were incorrectly redirecting to the English version
instead of staying within the same language directory.

The problem was in the isArticleLink() function which didn't properly
recognize HTML files with anchors as article links. Now it splits the URL
on '#' and checks the base URL.

Before: webgpu-fundamentals.html#anchor -> ../webgpu-fundamentals.html#anchor (English)
After:  webgpu-fundamentals.html#anchor -> webgpu-fundamentals.html#anchor (Same language)

🤖 Generated with [Claude Code](https://claude.ai/code)

Author: ryuchihoon

build.js

@@ -522,7 +522,9 @@ const Builder = function(outBaseDir, options) {
   }
 
   function isArticleLink(url) {
-    return !url.includes('/') && url.endsWith('.html');
+    // Handle both regular html links and html links with anchors in them
+    const baseUrl = url.split('#')[0];
+    return !baseUrl.includes('/') && baseUrl.endsWith('.html');
   }
 
   // Try top fix relative links. This *should* only