style: standardize VBA property and method name casing

Standardize all VBA property and method names to lowercase for consistent code style:
- Err object: Err.Description → err.Description, Err.Number → err.Number
- Collection properties: .Count → .count
- Range properties: .Rows.Count → .Rows.count, .Row → .row
- Dictionary methods: .Keys → .keys, .Exists → .exists
- Worksheet properties: .Sheets.Count → .Sheets.count
- Fix typo: Thisworkbook.Path → ThisWorkbook.Path

VBA is case-insensitive, but consistent lowercase convention improves readability.

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

VBA_BOMConverter/Modules/M02_DataIO.bas

@@ -154,7 +154,7 @@ Public Sub WriteCategoryToNewBook(catData As Object)
     Application.DisplayAlerts = True
 
     ' 6. 保存工作簿为 BOM库.xlsx
-    savePath = Thisworkbook.Path & Application.PathSeparator & "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