Core: Fix build error without JS engine

.changeset/olive-coins-rhyme.md

@@ -0,0 +1,5 @@
+---
+'fumadocs-core': patch
+---
+
+Fix build error without JS engine

packages/core/src/mdx-plugins/rehype-code.ts

@@ -9,6 +9,7 @@ import type { Processor, Transformer } from 'unified';
 import {
   getSingletonHighlighter,
   createJavaScriptRegexEngine,
+  createWasmOnigEngine,
   type ShikiTransformer,
   bundledLanguages,
   type BuiltinTheme,
@@ -159,7 +160,7 @@ export function rehypeCode(
   const highlighter = getSingletonHighlighter({
     engine: codeOptions.experimentalJSEngine
       ? createJavaScriptRegexEngine()
-      : undefined,
+      : createWasmOnigEngine(),
     themes: themeItems.filter(Boolean) as BuiltinTheme[],
     langs: codeOptions.langs ?? Object.keys(bundledLanguages),
   });