dsh-file-uploads: Upload any local files in DeepSeek Harness Web

`dsh-file-uploads` is an MIT-licensed plugin for the DeepSeek Harness Web interface, designed to break through the current limitation of only supporting raster image attachments. The plugin allows users to upload arbitrary local files and attaches file paths to the prompt in the form of absolute paths readable by the model via a built-in serializer during message submission, without interfering with the text editor content. It is compatible with DeepSeek Harness `0.1.0-rc.6` and Node.js 22+. Core features include: * Support for multi-file uploads with card display above the Composer; * Default storage in the `$DSH_HOME/uploads` directory, with support for configuring storage paths, single-file quotas, and total size quotas via environment variables; * A filename conflict prevention mechanism; * Provision of options in settings.