refactor: 统一导出文件命名规则，使用文件前缀变量

提取file_prefix变量统一管理导出文件的命名前缀，
确保所有导出的Excel和DXF文件使用一致的命名规则，
提升代码可维护性和文件命名的一致性。

gui.py

@@ -212,11 +212,12 @@ def index():
         if not state["results"] or not refs["export_row"]:
             return
 
-        # 获取带 _result 后缀的文件名
+        # 获取文件名基础前缀
+        file_prefix = "wind_farm"
         download_name = "wind_farm_design_result.xlsx"
         if state.get("original_filename"):
-            name_no_ext = os.path.splitext(state["original_filename"])[0]
+            file_prefix = os.path.splitext(state["original_filename"])[0]
-            download_name = f"{name_no_ext}_result.xlsx"
+            download_name = f"{file_prefix}_result.xlsx"
 
         # 寻找推荐方案：优先 Scenario 1 的最低成本，否则取全局最低成本
         scenario1_results = [r for r in state["results"] if "Scenario 1" in r["name"]]
@@ -241,7 +242,7 @@ def index():
                             if c.isalnum() or c in (" ", "-", "_")
                         ]
                     ).strip()
-                    dxf_name = f"design_best_{safe_name}.dxf"
+                    dxf_name = f"{file_prefix}_best_{safe_name}.dxf"
 
                     export_to_dxf(
                         best_res["turbines"],
@@ -278,7 +279,7 @@ def index():
                             if c.isalnum() or c in (" ", "-", "_")
                         ]
                     ).strip()
-                    dxf_name = f"design_{safe_name}.dxf"
+                    dxf_name = f"{file_prefix}_{safe_name}.dxf"
 
                     export_to_dxf(
                         selected_res["turbines"],
@@ -308,21 +309,17 @@ def index():
                 import zipfile
 
                 # 1. 确定文件名
-                zip_filename = "all_designs_result.zip"
+                zip_filename = f"{file_prefix}_all_results.zip"
-                excel_result_name = "wind_farm_design_result.xlsx"
+                excel_result_name = f"{file_prefix}_summary.xlsx"
 
                 # 推断 main.py 生成的原始 Excel 路径
                 generated_excel_path = "wind_farm_design.xlsx"
 
                 if state.get("original_filename"):
-                    name_no_ext = os.path.splitext(state["original_filename"])[0]
-                    zip_filename = f"{name_no_ext}_result.zip"
-                    excel_result_name = f"{name_no_ext}_result.xlsx"
-
                     if state.get("excel_path"):
                         dir_name = os.path.dirname(state["excel_path"])
                         generated_excel_path = os.path.join(
-                            dir_name, f"{name_no_ext}_design.xlsx"
+                            dir_name, f"{file_prefix}_design.xlsx"
                         )
 
                 try:
@@ -353,7 +350,7 @@ def index():
                                     if c.isalnum() or c in (" ", "-", "_")
                                 ]
                             ).strip()
-                            dxf_name = f"design_{safe_name}.dxf"
+                            dxf_name = f"{file_prefix}_{safe_name}.dxf"
                             export_to_dxf(
                                 res["turbines"],
                                 state["substation"],