feat(oa): add initiator system field to condition branches

Allow __initiator__ contains matching in publish validation and the
flow designer candidate list, excluding it from form useInCondition locks.

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

docs/superpowers/specs/2026-07-30-oa-initiator-condition-design.md

@@ -3,7 +3,7 @@
 **日期：** 2026-07-30  
 **范围：** `web-admin` 审批设计器步骤 3（流程设计）条件编辑；`backend` 条件匹配、发布校验、流程预览  
 **关联：** `docs/superpowers/specs/2026-07-15-oa-condition-from-form-design.md`（原非目标「系统变量」本期落地发起人）；`docs/superpowers/specs/2026-07-30-oa-person-select-design.md`（contains / 人员多选 UI 可复用）  
-**状态：** 已评审待实现  
+**状态：** 已实现  
 
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