Add support for Zip export #68
Description
The BookStack API now supports exporting documents as Zip files (https://demo.bookstackapp.com/api/docs#pages-exportZip), would it be possible for bookstack-file-exporter to support those too?
Right now, adding - zip in the formats config raises this exception
2025-09-09 09:16:50 [ERROR] Yaml configuration failed schema validation
Traceback (most recent call last):
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Scripts\bookstack-file-exporter.exe\__main__.py", line 10, in <module>
sys.exit(main())
~~~~^^
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Lib\site-packages\bookstack_file_exporter\__main__.py", line 12, in main
run.entrypoint(args)
~~~~~~~~~~~~~~^^^^^^
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Lib\site-packages\bookstack_file_exporter\run.py", line 19, in entrypoint
config = ConfigNode(args)
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Lib\site-packages\bookstack_file_exporter\config_helper\config_helper.py", line 56, in __init__
self.user_inputs = self._generate_config(args.config_file)
~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Lib\site-packages\bookstack_file_exporter\config_helper\config_helper.py", line 78, in _generate_config
raise err
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Lib\site-packages\bookstack_file_exporter\config_helper\config_helper.py", line 74, in _generate_config
user_inputs = models.UserInput(**yaml_input)
File "C:\Users\p0129085\AppData\Local\uv\cache\archive-v0\-Xj_ItJTK_SRyXAPn6O7T\Lib\site-packages\pydantic\main.py", line 253, in __init__
validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
pydantic_core._pydantic_core.ValidationError: 1 validation error for UserInput
formats.4
Input should be 'markdown', 'html', 'pdf' or 'plaintext' [type=literal_error, input_value='zip', input_type=str]
For further information visit https://errors.pydantic.dev/2.11/v/literal_error