修复Dify对话记录加载问题：移除user参数，由后端自动管理

问题描述：
- 用户登录后无法加载历史对话记录
- 根本原因：前端传递的user值与实际用户不一致，导致Dify无法找到对应的对话

解决方案：
- 后端已实现user字段自动填充功能（v1.2.7-post2）
- 前端采用方案A：完全移除user参数传递
- 让后端从JWT中自动提取username并管理user字段

修改内容：
1. dify-client.server.ts
   - 移除所有方法的user参数
   - GET请求移除user查询参数
   - POST/DELETE请求移除user字段
   - 移除generateUserId工具函数

2. 所有API路由
   - 移除getSessionInfo中的user解构
   - 移除difyClient方法调用中的user参数传递
   - 日志中移除user信息输出

影响接口：
- GET /dify/conversations - 会话列表
- GET /dify/messages - 消息历史
- POST /dify/chat-messages - 发送消息
- POST /dify/conversations/{id}/name - 重命名会话
- DELETE /dify/conversations/{id} - 删除会话
- POST /dify/messages/{id}/feedbacks - 消息反馈

参考文档：docs/dify-frontend-user-field-guide.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/services/dify-client.server.ts

@@ -81,15 +81,11 @@ const difyFetch = async (endpoint: string, options: RequestInit = {}, jwt?: stri
     return response;
 };
 
-// 生成用户ID
-const generateUserId = (sessionId: string) => {
-    return `user_${DIFY_CONFIG.APP_ID}:${sessionId}`;
-};
-
 // Dify API 客户端 - 所有方法都需要传入 JWT
+// 注意：user 参数已移除，由后端自动从 JWT 中提取 username
 export const difyClient = {
     // 获取应用参数
-    async getApplicationParameters(user: string, jwt?: string) {
+    async getApplicationParameters(jwt?: string) {
         const response = await difyFetch('parameters', {
             method: 'GET',
         }, jwt);
@@ -97,9 +93,8 @@ export const difyClient = {
     },
 
     // 获取会话列表
-    async getConversations(user: string, jwt?: string) {
+    async getConversations(jwt?: string) {
         const params = new URLSearchParams({
-            user,
             limit: '100',
             first_id: '',
         });
@@ -111,9 +106,8 @@ export const difyClient = {
     },
 
     // 获取会话消息
-    async getConversationMessages(user: string, conversationId: string, jwt?: string) {
+    async getConversationMessages(conversationId: string, jwt?: string) {
         const params = new URLSearchParams({
-            user,
             conversation_id: conversationId,
             limit: '20',
             last_id: '',
@@ -129,7 +123,6 @@ export const difyClient = {
     async createChatMessage(
         inputs: Record<string, any>,
         query: string,
-        user: string,
         responseMode: string = 'streaming',
         conversationId?: string,
         files?: any[],
@@ -138,7 +131,7 @@ export const difyClient = {
         const body = {
             inputs,
             query,
-            user,
+            // user 字段已移除，后端会自动从 JWT 中提取 username
             response_mode: responseMode,
             conversation_id: conversationId,
             files: files || [],
@@ -147,7 +140,6 @@ export const difyClient = {
         console.log('🌐 [DifyClient] 发送聊天消息:', {
             queryLength: query.length,
             queryPreview: query.substring(0, 100) + (query.length > 100 ? '...' : ''),
-            user,
             responseMode,
             conversationId,
             hasInputs: !!inputs && Object.keys(inputs).length > 0,
@@ -181,11 +173,11 @@ export const difyClient = {
     },
 
     // 重命名会话
-    async renameConversation(conversationId: string, name: string, user: string, autoGenerate: boolean = false, jwt?: string) {
+    async renameConversation(conversationId: string, name: string, autoGenerate: boolean = false, jwt?: string) {
         const body = {
             name,
             auto_generate: autoGenerate,
-            user,
+            // user 字段已移除，后端会自动从 JWT 中提取 username
         };
 
         const response = await difyFetch(`conversations/${conversationId}/name`, {
@@ -196,10 +188,9 @@ export const difyClient = {
     },
 
     // 删除会话
-    async deleteConversation(conversationId: string, user: string, jwt?: string) {
-        const body = {
-            user,
-        };
+    async deleteConversation(conversationId: string, jwt?: string) {
+        // user 字段已移除，后端会自动从 JWT 中提取 username
+        const body = {};
 
         const response = await difyFetch(`conversations/${conversationId}`, {
             method: 'DELETE',
@@ -209,10 +200,10 @@ export const difyClient = {
     },
 
     // 更新消息反馈
-    async updateMessageFeedback(messageId: string, rating: 'like' | 'dislike' | null, user: string, jwt?: string) {
+    async updateMessageFeedback(messageId: string, rating: 'like' | 'dislike' | null, jwt?: string) {
         const body = {
             rating,
-            user,
+            // user 字段已移除，后端会自动从 JWT 中提取 username
         };
 
         const response = await difyFetch(`messages/${messageId}/feedbacks`, {
@@ -225,6 +216,5 @@ export const difyClient = {
 
 // 工具函数
 export const difyUtils = {
-    generateUserId,
     getConfig: () => DIFY_CONFIG,
 };