feat(vocab): implement upcoming vocabulary review tracking and update UI accordingly

backend/services/vocabService.js

@@ -2031,6 +2031,21 @@ export default class VocabService {
       this._isTrainableSrsPair(item)
       && (!validKeys.size || validKeys.has(String(item.itemKey || '').trim()))
     );
+    const scheduledRows = await VocabSrsItem.findAll({
+      where: { userId: user.id, courseId: Number(course.id) },
+      order: [['nextDueAt', 'ASC']]
+    });
+    const upcomingByDate = new Map();
+    scheduledRows
+      .filter((item) => (
+        this._isTrainableSrsPair(item)
+        && (!validKeys.size || validKeys.has(String(item.itemKey || '').trim()))
+        && new Date(item.nextDueAt).getTime() > now.getTime()
+      ))
+      .forEach((item) => {
+        const date = new Date(item.nextDueAt).toISOString().slice(0, 10);
+        upcomingByDate.set(date, (upcomingByDate.get(date) || 0) + 1);
+      });
     const rows = validDueRows.slice(0, limit);
     const totalDueCount = validDueRows.length;
 
@@ -2046,6 +2061,7 @@ export default class VocabService {
       totalDueCount,
       dailyLimit: DAILY_SRS_LIMIT,
       limit,
+      upcoming: Array.from(upcomingByDate, ([date, count]) => ({ date, count })).slice(0, 6),
       items: rows.map((item) => ({
         itemKey: item.itemKey,
         courseId: item.courseId,