refactor: rename Chinese-named Python files to English

Rename utility files to use English names for better cross-platform compatibility:
- utils/离散备料计划维护数据提取.py → utils/discrete_material_plan_extractor.py
- utils/离散备料计划维护数据清理.py → utils/discrete_material_plan_cleaner.py

Update all import statements across the codebase and documentation references.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

gui/data_extraction_tab.py

@@ -162,7 +162,7 @@ class DataExtractionTab(ttk.Frame):
                 temp_file = f.name
                 f.write('\n'.join(production_ids))
 
-            from utils.离散备料计划维护数据提取 import DiscreteMaterialPlanExtractor
+            from utils.discrete_material_plan_extractor import DiscreteMaterialPlanExtractor
             self.extractor = DiscreteMaterialPlanExtractor(
                 username=self.config.get("erp.username"),
                 password=self.config.get("erp.password"),