feat(crm): sync contract number date segment with sign date

Align standard contract nos on create/update (keep seq, bump on collision),
preview the change in contract forms, and sync name parentheses.

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

docs/superpowers/specs/2026-08-03-crm-contract-no-follow-sign-date-design.md

@@ -2,7 +2,7 @@
 
 **日期**：2026-08-03  
 **范围**：`web-admin` 合同管理新增/编辑；`backend` 合同 create/update（草稿）  
-**状态**：已评审，待实现
+**状态**：已实现
 
 ## 背景