feat(referral): 将推荐链最大深度从10层提升到1000层

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

backend/services/referral-service/src/domain/services/referral-chain.service.ts

@@ -7,7 +7,7 @@ import { ReferralChain } from '../value-objects';
  */
 @Injectable()
 export class ReferralChainService {
-  private static readonly MAX_DEPTH = 10;
+  private static readonly MAX_DEPTH = 1000;
 
   /**
    * 构建新用户的推荐链

backend/services/referral-service/src/domain/value-objects/referral-chain.vo.ts

@@ -3,7 +3,7 @@
  * 存储从直接推荐人到根节点的用户ID列表
  */
 export class ReferralChain {
-  private static readonly MAX_DEPTH = 10;
+  private static readonly MAX_DEPTH = 1000;
 
   private constructor(public readonly chain: bigint[]) {
     if (chain.length > ReferralChain.MAX_DEPTH) {