docs: expand AutoBOM architecture and implementation details

Refine project overview to include specific business context (Blaidy Company) and the main workbook file. Restructure the architecture section into a layered object-oriented design (Data, Processing, Application layers) and define the responsibilities of core VBA classes.

Add new technical documentation sections covering:
- Model number format parsing structure
- Condition expression language syntax
- Category hierarchy logic and picking strategies
- Material matching pipeline flow

Include VBA code examples for key methods such as CollectAllMaterials and GetMaterialsByCategoryAndModel to illustrate recursive traversal and material retrieval logic. Clarify the structure of key Excel configuration sheets.

VBA/ClassModules/clsCategory.cls

@@ -6,19 +6,19 @@ 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 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
+    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
+    materials.Add mat, mat.code
 End Sub
 
 ' 添加子类别
@@ -30,7 +30,7 @@ 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)
+    Set GetMaterial = materials(code)
     On Error GoTo 0
 End Function