feat(db): add father/newborn customer ids on protocol parties

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/sql/migrations/2026-10-07-party-father-newborn-customer-id.sql

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+-- 采集协议当事人：父亲/子女客户 ID（母亲沿用 customer_id）
+ALTER TABLE biz_protocol_party_customer
+  ADD COLUMN father_customer_id VARCHAR(64) DEFAULT NULL COMMENT '父亲客户ID' AFTER customer_id,
+  ADD COLUMN newborn_customer_id VARCHAR(64) DEFAULT NULL COMMENT '子女客户ID' AFTER father_customer_id;
+
+-- 科研捐赠当事人：同上
+ALTER TABLE biz_research_donation_party
+  ADD COLUMN father_customer_id VARCHAR(64) DEFAULT NULL COMMENT '父亲客户ID' AFTER customer_id,
+  ADD COLUMN newborn_customer_id VARCHAR(64) DEFAULT NULL COMMENT '子女客户ID' AFTER father_customer_id;