dsh-shell-command: Adding /! Command Analysis and /terminal Session Referencing to DSH

dsh-shell-command is an MIT-licensed plugin for DeepSeek Harness (DSH), designed to address the need to hand over Shell command results to the model for analysis. It provides two core entry points: `/!` and `/terminal`. `/!` is used to run a single command in the session workspace, automatically handling output boundaries and sending them to the model for immediate analysis, making it suitable for scenarios such as checking disk usage, viewing logs, or analyzing build results. `/terminal` opens an interactive PTY terminal with session and history tabs, supporting multi-step debugging; after executing operations in the terminal, users can select one or more session records from the history, add notes, and send them to the model for analysis, making it ideal for exploratory operations and multi-session comparisons. This plugin is applicable to the dsh CLI environment and Node 2.