feat: 方案对比结果表格新增总长度列

- 在方案对比结果中新增'总长度(m)'列
- 自动计算每个方案的海缆总长度
- 支持按总长度排序，方便方案比选

gui.py

@@ -798,10 +798,14 @@ def index():
                     elif "No Max" in original_name:
                         note += "不包含可选电缆型号，且可使用的最大截面电缆降一档截面。"
 
+                    # 计算总长度
+                    total_length = sum(d["length"] for d in res["eval"]["details"])
+
                     row_dict = {
                         "name": name_display,
                         "cost_wan": f"{res['cost'] / 10000:.2f}",
                         "loss_kw": f"{res['loss']:.2f}",
+                        "total_length": f"{total_length:.2f}",
                         "note": note,
                         "original_name": res["name"],
                     }
@@ -950,13 +954,18 @@ def index():
                                                 "field": "loss_kw",
                                                 "sortable": True,
                                             },
+                                            {
+                                                "name": "total_length",
+                                                "label": "总长度 (m)",
+                                                "field": "total_length",
+                                                "sortable": True,
+                                            },
                                             {
                                                 "name": "note",
                                                 "label": "备注",
                                                 "field": "note",
                                                 "align": "left",
-                        },
-                    ]
+                                            },                    ]
                     # 使用内置的 selection='single' 结合行点击事件实现背景高亮
                     # 这样可以完全由 Python 事件逻辑控制，不依赖 CSS 伪类
                     refs["results_table"] = ui.table(