feat: 订单创建时快照买家手机号/昵称和套餐类型

新增字段：
- tb_order: buyer_phone, buyer_nickname（个人客户下单时快照）
- tb_order_item: package_type（套餐类型快照）

后台订单列表支持按 buyer_phone 精确过滤查询。

OpenSpec: order-buyer-snapshot

migrations/000112_add_buyer_snapshot_to_order.down.sql

@@ -0,0 +1,8 @@
+DROP INDEX IF EXISTS idx_order_buyer_phone;
+
+ALTER TABLE tb_order
+    DROP COLUMN IF EXISTS buyer_phone,
+    DROP COLUMN IF EXISTS buyer_nickname;
+
+ALTER TABLE tb_order_item
+    DROP COLUMN IF EXISTS package_type;

migrations/000112_add_buyer_snapshot_to_order.up.sql

@@ -0,0 +1,16 @@
+-- 订单买家快照字段：buyer_phone、buyer_nickname（下单时快照买家手机号和昵称）
+-- 套餐类型快照字段：package_type（下单时快照套餐类型，避免套餐删除后信息丢失）
+
+ALTER TABLE tb_order
+    ADD COLUMN IF NOT EXISTS buyer_phone    VARCHAR(20)  NULL,
+    ADD COLUMN IF NOT EXISTS buyer_nickname VARCHAR(100) NULL;
+
+COMMENT ON COLUMN tb_order.buyer_phone    IS '下单时买家主手机号快照（个人客户有值，代理商留空）';
+COMMENT ON COLUMN tb_order.buyer_nickname IS '下单时买家昵称快照（个人客户有值，代理商留空）';
+
+CREATE INDEX IF NOT EXISTS idx_order_buyer_phone ON tb_order (buyer_phone) WHERE buyer_phone IS NOT NULL;
+
+ALTER TABLE tb_order_item
+    ADD COLUMN IF NOT EXISTS package_type VARCHAR(20) NULL;
+
+COMMENT ON COLUMN tb_order_item.package_type IS '套餐类型快照 (formal:正式套餐, addon:加油包)';