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_reimbursement_endpoints.py

@@ -345,9 +345,17 @@ def test_approve_claim_endpoint_routes_direct_manager_claim_to_finance_review()
     assert any(
         item["source"] == "manual_approval"
         and item["opinion"] == "情况属实，同意报销。"
+        and item["operator"] == "李经理"
         and item["next_approval_stage"] == "财务审批"
         for item in payload["risk_flags_json"]
     )
+    approval_events = [
+        item
+        for item in payload["risk_flags_json"]
+        if item["source"] == "manual_approval"
+    ]
+    assert approval_events[0]["operator"] == "李经理"
+    assert "manager-approve-api@example.com" not in approval_events[0]["message"]
 
 
 def test_claim_item_pdf_attachment_preview_returns_generated_image(monkeypatch, tmp_path) -> None: