编辑器体验改进

- 导入文件后直接关闭弹窗 + toast 提示导入数量
- 自动布局改为按出口顺序的子树居中：选项1/2/3 分支顺序正确且对齐

web/static/style.css

@@ -114,6 +114,13 @@ button.mini { padding:2px 8px; font-size:12px; }
 #drawflow .connection .main-path { stroke:#7a96c8; stroke-width:2.4px; }
 #drawflow .connection .main-path:hover { stroke:#e6c878; }
 
+/* ---- toast ---- */
+#toast { position:fixed; left:50%; bottom:38px; transform:translateX(-50%) translateY(10px);
+         background:#2a2316; color:#f3dca0; border:1px solid #6a5630; border-radius:7px;
+         padding:10px 18px; font-size:13.5px; box-shadow:0 4px 16px rgba(0,0,0,.5);
+         opacity:0; pointer-events:none; transition:.25s; z-index:9999; }
+#toast.show { opacity:1; transform:translateX(-50%) translateY(0); }
+
 /* ---- form ---- */
 .fld { margin:9px 0; }
 .fld > label { display:block; font-size:12px; color:#9a8f7e; margin-bottom:3px; }