LessXi/dsh-fluid-width: DSH Web GUI Chat Display Area Fluid Width

`LessXi/dsh-fluid-width` is a layout plugin for the DSH Web GUI designed to address the issue where the chat display area appears too narrow on wide screens due to a fixed width (defaulting to 748px). By overriding the CSS variable `--dsh-chat-content-width` to `min(100%, 2000px)`, the plugin enables the chat column, input box, and other content to adaptively flow with the window width, while retaining a default maximum width of 2000px. Users can also customize this value or switch to a fully fluid layout. The plugin is released under the MIT license, has zero dependencies, and requires no build scripts; it takes effect after restarting `dsh web` and refreshing the page. Its core mechanism combines static overrides with dynamic rewriting via `MutationObserver` as a mutual fallback.