dsh-codex-provider: Integrating OpenAI Codex into DSH via Device Code OAuth

dsh-codex-provider is a DeepSeek Harness (DSH) community plugin developed by Hu9956, designed to address users' desire to invoke the OpenAI Codex model via the DSH web interface without using an OpenAI API Key, while leveraging ChatGPT Plus/Pro subscription credits. Built on the DSH "everything is a plugin" philosophy, this plugin integrates with OpenAI accounts through a device code OAuth authorization flow, automatically handles the rotation and refresh of access tokens and refresh tokens, and activates the built-in `openai-codex` model routing within DSH. The plugin's main features include support for device code login, importing local Codex CLI login states, and providing a provider management interface.