dsh-plan-switch: One-click Switch Button for /plan in DSH Web Input Bar

dsh-plan-switch is a community plugin developed specifically for the DeepSeek Harness (DSH) web client, designed to optimize the Plan mode user experience. This plugin allows users to toggle Plan mode with a single click by clicking the checklist icon button at the left end of the input tool row, which executes the official `/plan` command, eliminating the hassle of manually typing commands. Its core mechanism aligns with the official logic: when Plan mode is activated, the button automatically hides, and the official plan card takes over the status display to avoid redundant indications; meanwhile, the button is disabled during command queuing to prevent accidental operations. The plugin adopts a pure client-side architecture, involves no data writing or storage, and adapts to both dark and light themes. Installation requires ensuring pnpm is in the PATH and executing the specified GitHub repository installation command.