fix(admin-service): 修复 referrerId 可能为 null 的 TypeScript 错误

- getAncestors 和 getDirectReferrals 中的 directReferralCounts
  groupBy 结果 referrerId 字段可能为 null
- 添加 filter 过滤 null 值，使用非空断言通过类型检查

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/admin-service/src/infrastructure/persistence/repositories/user-detail-query.repository.impl.ts

@@ -102,7 +102,11 @@ export class UserDetailQueryRepositoryImpl implements IUserDetailQueryRepository
     ]);
 
     const adoptionCountMap = new Map(adoptionCounts.map(a => [a.accountSequence, a._count.id]));
-    const directCountMap = new Map(directReferralCounts.map(d => [d.referrerId.toString(), d._count.userId]));
+    const directCountMap = new Map(
+      directReferralCounts
+        .filter(d => d.referrerId !== null)
+        .map(d => [d.referrerId!.toString(), d._count.userId])
+    );
 
     // 合并数据
     const referralMap = new Map(referrals.map((r) => [r.userId.toString(), r]));
@@ -175,7 +179,11 @@ export class UserDetailQueryRepositoryImpl implements IUserDetailQueryRepository
     ]);
 
     const adoptionCountMap = new Map(adoptionCounts.map(a => [a.accountSequence, a._count.id]));
-    const directCountMap = new Map(directReferralCounts.map(d => [d.referrerId.toString(), d._count.userId]));
+    const directCountMap = new Map(
+      directReferralCounts
+        .filter(d => d.referrerId !== null)
+        .map(d => [d.referrerId!.toString(), d._count.userId])
+    );
     const userMap = new Map(users.map((u) => [u.userId.toString(), u]));
 
     return directReferrals.map((ref) => {