dsh-airdrop: Drag files into DSH, AI reads them

dsh-airdrop is a web-based plugin for DSH designed to resolve file upload challenges. Users simply need to drag files or folders into the DSH window; attachments will be sent along with messages, and the AI will automatically read the content. The plugin supports attachments in any format without type restrictions and provides in-browser preview functionality. Files are stored only in a workspace isolated to the current session, ensuring they do not interfere with each other. For large files, the plugin supports chunked upload, resumable uploads, and automatic retries for gateway errors, with a single file limit of 20 GiB. Installation requires Node.js >= 22. You can enable it by adding the `dsh-universal-attachments` package via the `dsh plugin` command and restarting the service. For security reasons, it is recommended to access remotely via an SSH tunnel to avoid exposing the service directly to the public internet. Note that empty directories may not be preserved during use.