refactor: export form modules as .frm files to align with VBA conventions

Change form module export from .cls to .frm extension to match standard VBA file conventions and align with import_vba.py expectations. This eliminates ambiguity between class modules and form modules.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

extract_vba.py

@@ -253,7 +253,7 @@ class VBAExtractor:
             stream_path: 流路径
 
         Returns:
-            模块类型: Modules, ClassModules, DocumentModules
+            模块类型: Modules, ClassModules, DocumentModules, Forms
         """
         name_lower = module_name.lower()
 
@@ -269,6 +269,10 @@ class VBAExtractor:
         if name_lower.startswith('cls') or name_lower.startswith('class'):
             return CLASS_MODULE_DIR
 
+        # 窗体模块
+        if name_lower.startswith('userform') or name_lower.startswith('frm_') or name_lower.startswith('frm'):
+            return FORMS_DIR
+
         # 根据stream_path判断
         if stream_path:
             path_lower = stream_path.lower()
@@ -276,6 +280,8 @@ class VBAExtractor:
                 return DOCUMENT_MODULE_DIR
             elif 'class' in path_lower or 'cls' in path_lower:
                 return CLASS_MODULE_DIR
+            elif 'form' in path_lower or 'userform' in path_lower:
+                return FORMS_DIR
 
         # 默认为标准模块
         return STANDARD_MODULE_DIR
@@ -309,7 +315,12 @@ class VBAExtractor:
         }.get(module_type, self.modules_dir)
 
         # 确定文件扩展名
-        ext = '.cls' if module_type in [CLASS_MODULE_DIR, DOCUMENT_MODULE_DIR, FORMS_DIR] else '.bas'
+        if module_type == FORMS_DIR:
+            ext = '.frm'
+        elif module_type in [CLASS_MODULE_DIR, DOCUMENT_MODULE_DIR]:
+            ext = '.cls'
+        else:
+            ext = '.bas'
 
         # 清理文件名（移除已有扩展名）
         clean_name = module_name.replace('/', '_').replace('\\', '_')