fix: 上一题/下一题不再调 AI API，改为保存后关闭并推进索引

src/types/index.ts

@@ -83,6 +83,9 @@ export interface ElectronAPI {
     getData: () => Promise<any>
     exportJson: () => Promise<boolean>
     importJson: () => Promise<{ questions: QuestionItem[]; currentIndex: number } | null>
+    getNextIndex: () => Promise<number>
+    setNextIndex: (idx: number) => Promise<void>
+    resetNextIndex: () => Promise<void>
   }
   template: {
     list: () => Promise<unknown[]>