fix: repair 5 sites where StudentDingMapping.studentId was misused as User FK

- dingtalk.service.ts syncOneUser: query studentRepo (not userRepo) by mapping.studentId
- sync.service.ts importDingTalkUsers: skip User role lookup for existing mappings
- attendance.service.ts autoMatchDingRecords: use studentId directly, remove second-hop query
- schedule-sync.service.ts syncAll: skip teacher mapping block (deprecated)
- rbac.service.ts getUnboundUsers: return [] (method deleted in Task 4)

apps/server/src/sync/schedule-sync.service.ts

@@ -87,11 +87,8 @@ export class ScheduleSyncService {
     }
 
     // ── Step 2: 获取教师→钉钉用户ID映射 ──
-    const teacherIds = [...new Set(schedules.map((s) => s.teacherId!).filter(Boolean))];
-    const mappings = await this.studentDingMappingRepo.find({
-      where: { studentId: In(teacherIds) },
-    });
-    const userIdToDingId = new Map(mappings.map((m) => [m.studentId, m.dingUserId]));
+    // ponytail: teacher scheduling deprecated; StudentDingMapping.studentId is Student FK, not User
+    const userIdToDingId = new Map<number, string>();
 
     // ── Step 3: 按 (startTime, endTime) 创建/匹配班次 ──
     const shiftKey = (start: string, end: string) => `${start}-${end}`;