feat: 增加差旅报销标准测算和财务终审流程

新增差旅报销测算接口及 Spreadsheet 规则解析，审批流程拆分
直属领导审批与财务终审两阶段并细分权限，修复 PDF 文本层
缺失时自动回退 OCR，提交后清理关联会话，前端适配审批流
交互并补充单元测试。

server/tests/test_orchestrator_review_flow.py

@@ -11,6 +11,7 @@ from app.db.base import Base
 from app.models.employee import Employee
 from app.models.financial_record import ExpenseClaim, ExpenseClaimItem
 from app.schemas.orchestrator import OrchestratorRequest
+from app.services.agent_conversations import AgentConversationService
 from app.services.orchestrator import OrchestratorService
 
 
@@ -96,6 +97,8 @@ def test_review_next_step_run_submits_existing_claim_and_returns_draft_payload(
         assert claim.status == "submitted"
         assert claim.approval_stage == "直属领导审批"
         assert claim.submitted_at is not None
+        assert response.conversation_id
+        assert AgentConversationService(db).get_conversation(response.conversation_id) is None
 
 
 def test_review_next_step_blocked_returns_reasons_and_removes_next_step_action(
@@ -165,6 +168,8 @@ def test_review_next_step_blocked_returns_reasons_and_removes_next_step_action(
 
         assert response.status == "succeeded"
         assert result["draft_payload"]["status"] == "draft"
+        assert response.conversation_id
+        assert AgentConversationService(db).get_conversation(response.conversation_id) is not None
         assert "AI预审暂未通过" in result["answer"]
         assert "所属部门未完善" in result["answer"]
         assert "next_step" not in actions