feat: 重构报销单服务并完善前端提交与审核交互

重构 expense_claims 服务模块结构并优化差旅票据审核逻辑，
增强用户代理服务的票据类型识别，前端报销创建页面拆分为
附件模型和会话模型模块，重构提交编排器和草稿关联确认流
程，更新知识库索引，补充单元测试。

web/src/views/scripts/travelReimbursementConversationModel.js

@@ -167,6 +167,7 @@ export function createMessage(role, text, attachments = [], extras = {}) {
     draftPayload: null,
     reviewPayload: null,
     riskFlags: [],
+    pendingAttachmentAssociation: null,
     ...extras
   }
 }
@@ -666,6 +667,7 @@ export function serializeSessionMessages(messages) {
     draftPayload: message.draftPayload || null,
     reviewPayload: message.reviewPayload || null,
     riskFlags: Array.isArray(message.riskFlags) ? message.riskFlags : [],
+    pendingAttachmentAssociation: message.pendingAttachmentAssociation || null,
     assistantName: message.assistantName || '',
     isWelcome: Boolean(message.isWelcome),
     welcomeQuickActions: Array.isArray(message.welcomeQuickActions) ? message.welcomeQuickActions : []