feat(mining-wallet-service): add migration for SHARE_POOL_A and SHARE_POOL_B

Split the share pool into two accounts:
- SHARE_POOL_A: 100亿 for burning
- SHARE_POOL_B: 200万 for mining distribution
Total: 100.02亿

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

backend/services/mining-wallet-service/prisma/migrations/0002_split_share_pool/migration.sql

@@ -0,0 +1,14 @@
+-- ============================================================================
+-- 拆分积分股池: SHARE_POOL -> SHARE_POOL_A + SHARE_POOL_B
+-- SHARE_POOL_A: 100亿 (10,000,000,000) - 用于销毁
+-- SHARE_POOL_B: 200万 (2,000,000) - 用于挖矿分配
+-- 总计: 100.02亿 (10,002,000,000)
+-- ============================================================================
+
+-- 1. 添加新的枚举值
+ALTER TYPE "PoolAccountType" ADD VALUE IF NOT EXISTS 'SHARE_POOL_A';
+ALTER TYPE "PoolAccountType" ADD VALUE IF NOT EXISTS 'SHARE_POOL_B';
+
+-- 2. 如果存在旧的 SHARE_POOL 记录，需要手动迁移数据后删除
+-- 注意: PostgreSQL 不支持直接删除枚举值，如果需要删除旧值需要重建枚举
+-- 这里只添加新值，旧的 SHARE_POOL 保留兼容