feat: 完善报销单审批流程及退回原因追踪

新增直属领导审批通过接口和审批待办列表查询，报销单退回
支持原因码分类和审批环节标记，优化票据附件去重和路径
回退查找，前端新增退回原因对话框、审批收件箱和工作台
图标组件，补充工具函数和单元测试覆盖。

server/src/app/schemas/reimbursement.py

@@ -150,6 +150,11 @@ class ExpenseClaimActionResponse(BaseModel):
 
 class ExpenseClaimReturnPayload(BaseModel):
     reason: str | None = Field(default=None, max_length=500)
+    reason_codes: list[str] = Field(default_factory=list, max_length=10)
+
+
+class ExpenseClaimApprovalPayload(BaseModel):
+    opinion: str | None = Field(default=None, max_length=500)
 
 
 class ExpenseClaimAttachmentActionResponse(BaseModel):