实现对话记录页并对齐工作台三栏布局

完善会话列表筛选与摘要字段、归档接口；对话记录按效果图重构；工作台顶栏等高对齐；默认管理员账号改为 kefu_admin / kefu_admin123。

server/internal/handler/router.go

@@ -54,9 +54,11 @@ func SetupRoutes(r *gin.Engine, store storage.ObjectStorage, storageCfg config.S
 		sessions.GET("", session.List)
 		sessions.GET("/:id", session.Get)
 		sessions.POST("", session.Create)
+		sessions.POST("/batch-archive", session.BatchArchive)
 		sessions.POST("/:id/assign", session.Assign)
 		sessions.POST("/:id/transfer", session.Transfer)
 		sessions.POST("/:id/end", session.End)
+		sessions.POST("/:id/archive", session.Archive)
 		sessions.PUT("/:id/priority", session.UpdatePriority)
 		sessions.POST("/:id/messages", session.SendMessage)
 		sessions.POST("/:id/read", session.MarkRead)