DSH-BTW: DSH Bypass Q&A Plugin

`dsh-btw` is a side-channel Q&A plugin for DSH, designed to address the need for ad-hoc questions during the main task without disturbing the main model's context. Through the `/btw` command and a centered pop-up panel, it provides an independent session branch for read-only Q&A. Core features include: incremental synchronization of the main conversation history for multi-turn dialogue, clearing branches, and independent maintenance per session; branches respond in read-only mode, with the tool allowlist restricted to read, glob, grep, read_image, and web_search, rejecting operations such as file writing and command execution; branches do not enter the main LLM context and are not displayed as sub-agents. Installation requires the dsh CLI and pnpm to be installed locally, followed by executing specific commands to add the plugin and restarting the `dsh web` process. The applicable scenario is for DSH Web users to retain read-only retrieval capabilities while avoiding pollution of the main context.