feat: 新增风险图谱算法与系统仪表盘及操作反馈体系

后端新增风险图谱算法模块、风险观察与反馈服务、规则 DSL
校验器和可解释性引擎，完善系统仪表盘和财务仪表盘统计，
优化 agent 运行和编排执行链路，清理旧开发文档，前端新增
系统趋势、负载热力图等多种仪表盘图表组件，完善操作反馈
对话框和工作台日期选择器，优化报销创建和审批详情交互，
补充单元测试覆盖。

server/src/app/services/audit.py

@@ -1,7 +1,8 @@
 from __future__ import annotations
 
-import uuid
-from typing import Any
+import uuid
+from datetime import UTC, datetime
+from typing import Any
 
 from sqlalchemy.orm import Session
 
@@ -47,15 +48,16 @@ class AuditLogService:
         after_json: dict[str, Any] | None = None,
         request_id: str | None = None,
     ) -> AuditLog:
-        log = AuditLog(
-            actor=actor,
-            action=action,
-            resource_type=resource_type,
-            resource_id=resource_id,
-            before_json=before_json,
-            after_json=after_json,
-            request_id=request_id or uuid.uuid4().hex,
-        )
+        log = AuditLog(
+            actor=actor,
+            action=action,
+            resource_type=resource_type,
+            resource_id=resource_id,
+            before_json=before_json,
+            after_json=after_json,
+            request_id=request_id or uuid.uuid4().hex,
+            created_at=datetime.now(UTC),
+        )
         created = self.repository.create(log)
         logger.info(
             "Created audit log id=%s action=%s resource=%s:%s",