fix(pre-planting): 修复推荐链 API 调用的 URL 路径和返回格式解析

1. URL: /referrals/:id/chain → /referral/chain/:id（与正常认种对齐）
2. 返回格式: 正确解析 { ancestors: [{accountSequence, hasPlanted}] }
   之前错误期望 { directReferrer: {...} }，导致有推荐人也被当成无推荐人

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/services/planting-service/src/pre-planting/infrastructure/external/pre-planting-referral.client.ts

@@ -11,6 +11,17 @@ export interface ReferralChainInfo {
   } | null;
 }
 
+/**
+ * referral-service /api/v1/referral/chain/:accountSequence 的实际返回格式
+ */
+interface ReferralChainApiResponse {
+  ancestors: Array<{
+    userId: string;
+    accountSequence: string;
+    hasPlanted: boolean;
+  }>;
+}
+
 @Injectable()
 export class PrePlantingReferralClient {
   private readonly logger = new Logger(PrePlantingReferralClient.name);
@@ -27,18 +38,43 @@ export class PrePlantingReferralClient {
 
   /**
    * 获取直接推荐人信息
+   *
+   * [2026-03-01] 修复：
+   * 1. URL 路径修正：/api/v1/referral/chain/:accountSequence（之前错误地用了 /referrals/:accountSequence/chain）
+   * 2. 返回格式修正：referral-service 返回 { ancestors: [{userId, accountSequence, hasPlanted}] }，
+   *    之前错误地期望 { directReferrer: {accountSequence, hasPlanted} }
+   * 3. ancestors[0] 即为直推人（直接推荐人）
    */
   async getReferralChain(accountSequence: string): Promise<ReferralChainInfo> {
     try {
       const response = await firstValueFrom(
-        this.httpService.get<ReferralChainInfo>(
-          `${this.baseUrl}/api/v1/referrals/${accountSequence}/chain`,
+        this.httpService.get<ReferralChainApiResponse>(
+          `${this.baseUrl}/api/v1/referral/chain/${accountSequence}`,
         ),
       );
-      return response.data;
+
+      const ancestors = response.data.ancestors || [];
+      if (ancestors.length === 0) {
+        this.logger.log(
+          `No referrer found for ${accountSequence} (empty ancestors)`,
+        );
+        return { accountSequence, directReferrer: null };
+      }
+
+      // ancestors[0] 为直推人
+      const directReferrer = ancestors[0];
+      this.logger.log(
+        `Referrer for ${accountSequence}: ${directReferrer.accountSequence} (hasPlanted=${directReferrer.hasPlanted})`,
+      );
+
+      return {
+        accountSequence,
+        directReferrer: {
+          accountSequence: directReferrer.accountSequence,
+          hasPlanted: directReferrer.hasPlanted ?? false,
+        },
+      };
     } catch (error) {
-      // 404 = 用户无推荐关系，属于正常情况（如测试账号、直接注册用户）
-      // 返回空推荐链而非抛错，避免阻断购买流程
       if (error?.response?.status === 404) {
         this.logger.warn(
           `No referral chain found for ${accountSequence}, proceeding without referrer`,