fix: send empty JSON body on convert to avoid body-parser 400

postJSON without options sends Content-Type: application/json with no
body; body-parser's BodyParserWrapper intercepts the resulting
SyntaxError and returns 400 before the route handler runs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/web/frontend/js/features/ide-react/hooks/use-convert-doc.ts

@@ -18,7 +18,9 @@ export default function useConvertDoc(
     setConverting(true)
     hideExportDocumentError()
     try {
-      await postJSON(`/project/${projectId}/doc/${docId}/convert/${type}`)
+      await postJSON(`/project/${projectId}/doc/${docId}/convert/${type}`, {
+        body: {},
+      })
       // File tree updates automatically via socket event
     } catch (err: any) {
       const errorMessage = err?.data?.error