feat: exam actions and data safety fixes

src/modules/textbooks/data-access.ts

@@ -65,7 +65,7 @@ let MOCK_KNOWLEDGE_POINTS: KnowledgePoint[] = [
 
 export async function getTextbooks(query?: string, subject?: string, grade?: string): Promise<Textbook[]> {
   await new Promise((resolve) => setTimeout(resolve, 500));
-  let results = [...MOCK_TEXTBOOKS];
+  const results = [...MOCK_TEXTBOOKS];
   // ... (filtering logic)
   return results;
 }