dsh-ui-mobile: Mobile Plugin for DeepSeek Harness Web Shell

`dsh-ui-mobile` is a mobile client plugin for DeepSeek Harness Web Shell, optimized for phone screens (widths below 768px), while desktop and tablet versions retain the native interface. This plugin aims to address operational friction on narrow screens by providing a drawer-style sidebar and detail panel, a bottom navigation bar, and a touch-friendly input area where the input box is fixed at the bottom of the visible area and the primary keyboard action is "Send." Additionally, it supports PWA installation, allowing users to add the app to their home screen for standalone launch, and can send Web Push notifications upon successful completion of Agent tasks. This plugin does not duplicate the Shell, modify the Harness source code, or alter model requests, system prompts, or session content, and has no impact on the KV Cache. Installation requires the `dsh plug