feat: auto-save output workbook as BOM库.xlsx and clean default sheets

- Delete default sheets (Sheet1, Sheet2, etc.) created by Workbooks.Add
- Save output workbook as BOM库.xlsx in the same directory as source file
- Auto-close workbook after saving
- Update completion message to show save path
- Use ThisWorkbook.Path to get source file directory

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

VBA_BOMConverter/Modules/M02_DataIO.bas

@@ -53,6 +53,8 @@ Public Sub WriteCategoryToNewBook(catData As Object)
     Dim i As Long, r As Long, c As Long
     Dim rowDict As Object
     Dim key As Variant
+    Dim savePath As String
+    Dim sheetToDelete As Worksheet
 
     If catData.count = 0 Then Exit Sub
 
@@ -142,7 +144,27 @@ Public Sub WriteCategoryToNewBook(catData As Object)
         End If
     Next catName
 
-    MsgBox "处理完成！", vbInformation
+    ' 5. 删除默认工作表（Workbooks.Add 创建的空白工作表）
+    Application.DisplayAlerts = False ' 禁用删除确认对话框
+    For Each sheetToDelete In newWb.Worksheets
+        If sheetToDelete.Name Like "Sheet*" Then
+            sheetToDelete.Delete
+        End If
+    Next sheetToDelete
+    Application.DisplayAlerts = True
+
+    ' 6. 保存工作簿为 BOM库.xlsx
+    savePath = Thisworkbook.Path & Application.PathSeparator & "BOM库.xlsx"
+
+    ' 如果文件已存在，先删除
+    If Dir(savePath) <> "" Then
+        Kill savePath
+    End If
+
+    newWb.SaveAs savePath, FileFormat:=xlOpenXMLWorkbook
+    newWb.Close SaveChanges:=False
+
+    MsgBox "处理完成！已保存至：" & vbCrLf & savePath, vbInformation
 End Sub
 
 Private Function SortHeaders(keys As Variant) As String()