feat: add core VBA source code modules

Add VBA directory with essential project code including:
- ClassModules: BomExtractor, BomItem, ConditionEvaluator, ProductModelParser
- Modules: MainModule, TestModule
- Forms and DocumentModules
- vba_metadata.json for module metadata

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

VBA/vba_metadata.json

@@ -0,0 +1,41 @@
+{
+  "source_file": "C:\\Users\\pengq\\Downloads\\AutoBOM\\AutoBOM\\YTHN-100_-_Claude3.xlsm",
+  "modules": {
+    "MainModule.bas": {
+      "name": "MainModule",
+      "type": "Modules",
+      "attributes": {},
+      "file": "Modules\\MainModule.bas"
+    },
+    "TestModule.bas": {
+      "name": "TestModule",
+      "type": "Modules",
+      "attributes": {},
+      "file": "Modules\\TestModule.bas"
+    },
+    "BomExtractor.cls": {
+      "name": "BomExtractor",
+      "type": "ClassModules",
+      "attributes": {},
+      "file": "ClassModules\\BomExtractor.cls"
+    },
+    "BomItem.cls": {
+      "name": "BomItem",
+      "type": "ClassModules",
+      "attributes": {},
+      "file": "ClassModules\\BomItem.cls"
+    },
+    "ConditionEvaluator.cls": {
+      "name": "ConditionEvaluator",
+      "type": "ClassModules",
+      "attributes": {},
+      "file": "ClassModules\\ConditionEvaluator.cls"
+    },
+    "ProductModelParser.cls": {
+      "name": "ProductModelParser",
+      "type": "ClassModules",
+      "attributes": {},
+      "file": "ClassModules\\ProductModelParser.cls"
+    }
+  }
+}