feat: 完善文档中心与报销申请交互及侧边栏重构

后端优化编排器报销查询和本体检测精度，增强报销单草稿保
存和附件回填逻辑，前端重构侧边栏组件支持折叠和图标导
航，完善文档中心状态筛选和详情提示，报销创建和审批详情
页优化会话管理和费用明细交互，新增助手应用服务和预设动
作工具函数，补充单元测试覆盖。

server/src/app/services/user_agent.py

@@ -44,6 +44,7 @@ from app.services.user_agent_documents import UserAgentDocumentService
 from app.services.user_agent_knowledge import UserAgentKnowledgeMixin
 
 from app.services.user_agent_constants import *
+from app.services.user_agent_application import UserAgentApplicationMixin
 from app.services.user_agent_response import UserAgentResponseMixin
 from app.services.user_agent_review_core import UserAgentReviewCoreMixin
 from app.services.user_agent_review_messages import UserAgentReviewMessageMixin
@@ -55,6 +56,7 @@ from app.services.user_agent_review_travel_receipts import UserAgentReviewTravel
 
 class UserAgentService(
     UserAgentResponseMixin,
+    UserAgentApplicationMixin,
     UserAgentKnowledgeMixin,
     UserAgentReviewCoreMixin,
     UserAgentReviewTravelPolicyMixin,
@@ -72,6 +74,12 @@ class UserAgentService(
     def respond(self, payload: UserAgentRequest) -> UserAgentResponse:
         AgentFoundationService(self.db).ensure_foundation_ready()
         citations = self._build_citations(payload)
+        risk_flags = self._resolve_risk_flags(payload)
+        if self._is_expense_application_request(payload):
+            return self._build_expense_application_response(
+                payload,
+                risk_flags=risk_flags,
+            )
         suggested_actions = self._build_suggested_actions(payload)
         if self._should_prompt_expense_scene_selection(payload):
             return UserAgentResponse(
@@ -84,7 +92,6 @@ class UserAgentService(
                 risk_flags=[],
                 requires_confirmation=False,
             )
-        risk_flags = self._resolve_risk_flags(payload)
         query_payload = self._build_query_payload(payload)
         draft_payload = (
             self._build_draft_payload(payload)