feat: 插件-工具合并 — 创建 pkg/plugins 共享模块并移除 tool-engine

- 新增 backend/pkg/plugins/ 共享模块：SDK 接口、PluginManager、ToolRegistry（含环形缓冲区调用日志）
- 13 个通用插件从 plugin-manager 迁移至共享模块（import 路径统一）
- ai-core 切换至共享 ToolRegistry，进程内执行（零网络开销），包装 6 个专属工具
- plugin-manager 迁移至共享模块，保留管理 REST API
- 新增 DevTools 插件管理面板（侧边栏 → 🔌 插件管理）
- 移除 tool-engine 服务（从 go.work、DevTools 配置、编译系统）
- 工具调用记录 API 从 Tool-Engine 迁至 AI-Core（/api/v1/tools/calls）
- ai-core ContextStore 启动时从 PostgreSQL 恢复会话历史
- 清理所有过时引用和备份文件

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/gateway/internal/handler/chat_handler.go

@@ -238,8 +238,8 @@ func (h *ChatHandler) streamResponse(client *ws.Client, mode string, reqBody []b
 	// 增大 scanner buffer 以处理大块 SSE 数据
 	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
 
-	// 通知前端 AI 开始生成回复
-	client.SendMessage(ws.ServerMessage{
+	// 通知所有客户端 AI 开始生成回复
+	h.broadcastToUser(client.UserID, ws.ServerMessage{
 		Type:      "stream_start",
 		MessageID: "msg_" + generateID(),
 		SessionID: client.SessionID,
@@ -336,7 +336,7 @@ func (h *ChatHandler) streamResponse(client *ws.Client, mode string, reqBody []b
 					Timestamp:  time.Now().UnixMilli(),
 					ClientInfo: clientInfo,
 				})
-				client.SendMessage(ws.ServerMessage{
+				h.broadcastToUser(client.UserID, ws.ServerMessage{
 					Type:       "response",
 					MessageID:  reviewMsgID,
 					Content:    rm.Content,
@@ -363,8 +363,8 @@ func (h *ChatHandler) streamResponse(client *ws.Client, mode string, reqBody []b
 					Text:  seg.Text,
 				})
 			}
-			// 发送断句事件给前端
-			client.SendMessage(ws.ServerMessage{
+			// 发送断句事件给所有客户端
+			h.broadcastToUser(client.UserID, ws.ServerMessage{
 				Type:      "stream_segments",
 				MessageID: msgID,
 				Segments:  segments,
@@ -408,7 +408,7 @@ func (h *ChatHandler) streamResponse(client *ws.Client, mode string, reqBody []b
 				Content: part,
 			})
 		}
-		client.SendMessage(ws.ServerMessage{
+		h.broadcastToUser(client.UserID, ws.ServerMessage{
 			Type:      "multi_message",
 			MessageID: msgID,
 			SessionID: client.SessionID,
@@ -419,8 +419,8 @@ func (h *ChatHandler) streamResponse(client *ws.Client, mode string, reqBody []b
 		})
 	}
 
-	// 发送 stream_end
-	client.SendMessage(ws.ServerMessage{
+	// 发送 stream_end 到所有客户端
+	h.broadcastToUser(client.UserID, ws.ServerMessage{
 		Type:      "stream_end",
 		MessageID: msgID,
 		SessionID: client.SessionID,
@@ -919,6 +919,16 @@ func randomStr(n int) string {
 	return hex.EncodeToString(b)[:n]
 }
 
+// broadcastToUser sends a server message to ALL connected clients for a user.
+func (h *ChatHandler) broadcastToUser(userID string, msg ws.ServerMessage) {
+	data, err := json.Marshal(msg)
+	if err != nil {
+		logger.Printf("[chat] 序列化广播消息失败: %v", err)
+		return
+	}
+	h.hub.SendToUser(userID, data)
+}
+
 // parseMultiMessage 检测并解析多消息格式
 // 如果文本包含空行分隔的多条消息，拆分为多条；否则返回单条
 func parseMultiMessage(text string) []string {