fix: remove double .json suffix in question file fetch URL

typeFile from meta.question_files already includes .json extension,
so appending .json again caused 404 (e.g. code_reading.json.json).

index.html

@@ -435,7 +435,7 @@ async function selectTopic(slug) {
 
     currentQuestions = [];
     for (const typeFile of meta.question_files) {
-      const qRes = await fetch(`${topicPath}/${typeFile}.json`);
+      const qRes = await fetch(`${topicPath}/${typeFile}`);
       const qData = await qRes.json();
       currentQuestions.push(...qData.questions);
     }