Add initial implementation of BOM management classes and data structure

- Created clsBOMManager for managing BOM data
- Added clsCategory and clsMaterialItem for category and material representation
- Implemented methods for loading and organizing BOM data from Excel
- Introduced .gitignore to exclude unnecessary files
- Added metadata JSON for module tracking

VBA/ClassModules/clsCategory.cls

@@ -0,0 +1,40 @@
+' ========================================
+' 类模块: clsCategory
+' 用途: 表示物料类别及其层级关系
+' ========================================
+Option Explicit
+
+Public categoryName As String
+Public ParentCategoryName As String
+Public Materials As Collection      ' 存储 clsMaterialItem 对象
+Public SubCategories As Collection  ' 存储子类别 clsCategory 对象
+Public IsLeafCategory As Boolean    ' 是否叶子类别(无子类别)
+
+Private Sub Class_Initialize()
+    Set Materials = New Collection
+    Set SubCategories = New Collection
+    IsLeafCategory = True
+End Sub
+
+' 添加物料
+Public Sub AddMaterial(mat As clsMaterialItem)
+    Materials.Add mat, mat.code
+End Sub
+
+' 添加子类别
+Public Sub AddSubCategory(cat As clsCategory)
+    SubCategories.Add cat, cat.categoryName
+    IsLeafCategory = False
+End Sub
+
+' 获取物料(按代号)
+Public Function GetMaterial(code As String) As clsMaterialItem
+    On Error Resume Next
+    Set GetMaterial = Materials(code)
+    On Error GoTo 0
+End Function
+
+' 检查是否有子类别
+Public Function HasSubCategories() As Boolean
+    HasSubCategories = (SubCategories.Count > 0)
+End Function