OnlyOffice Desktop Application Plugin

I currently use the LanguageTool plugin on OnlyOffice Writer desktop application for Linux but I would love to have a Harper plugin instead. This would allow grammar and spell checking for all my documents.

Start by reading OnlyOffice Writer's desktop plugin documentation for Linux and examining how the existing LanguageTool plugin provides grammar and spell checking. Define the integration scope and verify that a Harper plugin can check grammar and spelling across documents in the desktop application; completion means the plugin works in OnlyOffice Writer on Linux.

Written by the indexing model from the issue text.