fix(trading-service): add MINING_BLOCKCHAIN_SERVICE_URL to docker-compose

trading-service BlockchainClient defaults to http://localhost:3020 but
mining-blockchain-service runs on port 3026. Add the correct Docker
internal URL so the C2C Bot can reach the blockchain service.

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

backend/services/docker-compose.2.0.yml

@@ -114,6 +114,7 @@ services:
       MINING_SERVICE_URL: http://mining-service:3021
       AUTH_SERVICE_URL: http://auth-service:3024
       MINING_ADMIN_SERVICE_URL: http://mining-admin-service:3023
+      MINING_BLOCKCHAIN_SERVICE_URL: http://mining-blockchain-service:3026
       # JWT 配置 (与 auth-service 共享密钥以验证 token)
       JWT_SECRET: ${JWT_SECRET:-your-jwt-secret-change-in-production}
       # 做市商钱包 (MPC) - 初始化时写入数据库