fix: clear error messages between BOM extractions

Fix bug where error messages from previous orders were accumulating:
- Add ClearErrorMessages() public method to BomExtractor class
- Initialize pErrorMessages as new collection in ExtractBom()
- Replace commented-out pErrorMessages.Clear with proper initialization
- Ensures each order's error information is independent

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

VBA/ClassModules/BomExtractor.cls

@@ -112,6 +112,14 @@ Public Sub ClearExcludeCategories()
     Set pExcludeCategories = New collection
 End Sub
 
+'=====================================================================
+' 方法: ClearErrorMessages
+' 功能: 清空错误信息列表
+'=====================================================================
+Public Sub ClearErrorMessages()
+    Set pErrorMessages = New collection
+End Sub
+
 '=====================================================================
 ' 方法: ExtractBom
 ' 功能: 根据产品条件提取BOM
@@ -124,8 +132,7 @@ Public Function ExtractBom(productConditions As Object) As collection
     ' 清空结果
     Set pMatchedItems = New collection
     Set pRequiredCategories = New collection
-
-    'pErrorMessages.Clear
+    Set pErrorMessages = New collection
 
     ' 第一步:确定需要的类别
     DetermineRequiredCategories productConditions