feat: 归档旧迁移文件，创建初始化数据迁移和重置脚本

migrations/archive/000021_carrier_remove_channel_fields.down.sql

@@ -0,0 +1,12 @@
+-- 回滚：恢复 Carrier 表的 channel_name、channel_code 字段
+
+-- 添加 channel_name 字段
+ALTER TABLE tb_carrier ADD COLUMN channel_name VARCHAR(100);
+COMMENT ON COLUMN tb_carrier.channel_name IS '渠道名称';
+
+-- 添加 channel_code 字段
+ALTER TABLE tb_carrier ADD COLUMN channel_code VARCHAR(50);
+COMMENT ON COLUMN tb_carrier.channel_code IS '渠道编码';
+
+-- 重建联合唯一索引（carrier_type + channel_code，排除已删除记录）
+CREATE UNIQUE INDEX idx_carrier_type_channel ON tb_carrier(carrier_type, channel_code) WHERE deleted_at IS NULL;