fix(trading-service): 添加缺失的数据库字段迁移

Schema 中有但 migration 中缺失的字段：
- market_maker_configs: kava_wallet_address, mpc_username
- c2c_orders: seller_kava_address, bot_purchased, payment_tx_hash

这些字段缺失导致 500 错误：
"The column `market_maker_configs.kava_wallet_address` does not exist"

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

backend/services/trading-service/prisma/migrations/0003_add_kava_wallet_fields/migration.sql

@@ -0,0 +1,10 @@
+-- AlterTable: market_maker_configs
+-- Add kava wallet address and mpc username fields
+ALTER TABLE "market_maker_configs" ADD COLUMN "kava_wallet_address" VARCHAR(42);
+ALTER TABLE "market_maker_configs" ADD COLUMN "mpc_username" VARCHAR(100);
+
+-- AlterTable: c2c_orders
+-- Add bot purchase related fields
+ALTER TABLE "c2c_orders" ADD COLUMN "seller_kava_address" TEXT;
+ALTER TABLE "c2c_orders" ADD COLUMN "bot_purchased" BOOLEAN NOT NULL DEFAULT false;
+ALTER TABLE "c2c_orders" ADD COLUMN "payment_tx_hash" TEXT;