fix: SEED01用户accountSequence改为D25122100000格式

- identity-service: S0000000005 -> D25122100000
- referral-service: S0000000005 -> D25122100000
- 种子用户序号0，真实用户从1开始

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

backend/services/identity-service/prisma/seed.ts

@@ -51,7 +51,7 @@ const SYSTEM_ACCOUNTS = [
   },
   {
     userId: BigInt(5),
-    accountSequence: 'S0000000005',  // 种子用户
+    accountSequence: 'D25122100000',  // 种子用户 (序号0，真实用户从1开始)
     nickname: '种子用户',
     referralCode: 'SEED01',
     status: 'SYSTEM',

backend/services/referral-service/prisma/seed.ts

@@ -8,7 +8,7 @@ const prisma = new PrismaClient();
 // ============================================
 const SEED_USER = {
   userId: BigInt(5),
-  accountSequence: 'S0000000005',
+  accountSequence: 'D25122100000',  // 种子用户 (序号0，真实用户从1开始)
   myReferralCode: 'SEED01',
   usedReferralCode: null,  // 根节点无推荐人
   referrerId: null,        // 根节点