perf: 提升后端高并发承载能力

backend/internal/api/chat_handler.go

@@ -12,6 +12,8 @@ import (
 )
 
 var upgrader = websocket.Upgrader{
+	ReadBufferSize:  1024,
+	WriteBufferSize: 1024,
 	CheckOrigin: func(r *http.Request) bool {
 		return true // Allow all connections
 	},