feat: 新增预算费控模型与报销审批流引擎

后端新增预算费控服务和报销单审批流模块，引入申请人费用画像
算法，优化知识库 RAG 运行时和同步逻辑，完善报销单工作流常
量和明细同步，更新差旅报销规则电子表格，前端新增预算分析
组件和数字员工模型，完善审批对话框和洞察面板交互，优化侧
边栏和顶栏样式，补充单元测试。

server/src/app/services/user_agent.py

@@ -148,22 +148,7 @@ class UserAgentService(
                 requires_confirmation=payload.requires_confirmation,
             )
 
-        fast_knowledge_answer = self._build_fast_knowledge_answer(
-            payload,
-            citations=citations,
-        )
-        if fast_knowledge_answer:
-            return UserAgentResponse(
-                answer=fast_knowledge_answer,
-                citations=citations,
-                suggested_actions=suggested_actions,
-                query_payload=query_payload,
-                draft_payload=draft_payload,
-                review_payload=review_payload,
-                risk_flags=risk_flags,
-                requires_confirmation=payload.requires_confirmation,
-            )
-
+        # 知识库问答必须优先让模型基于召回证据组织答案，避免片段渲染抢答导致答非所问。
         fallback_answer = self._build_fallback_answer(
             payload,
             citations=citations,