refactor: migrate configuration to .env file for better environment management

- Replace hardcoded file paths with environment variables in extract_vba.py and import_vba.py
- Add .env file for local configuration (excluded from git via .gitignore)
- Add python-dotenv dependency for environment variable loading
- Maintain fallback to interactive mode when environment variables are not set

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

requirements.txt

@@ -5,3 +5,6 @@ pywin32>=306; sys_platform == 'win32'
 
 # olevba库方法 - 不需要Excel
 oletools>=0.60
+
+# 环境变量管理
+python-dotenv>=1.0.0