dsh-tool-highlight: Layered Syntax Highlighting for Bash/Pwsh and Read Output

`dsh-tool-highlight` is a plugin for DeepSeek Harness that adds VS Code Dark+–like layered syntax highlighting to the output of Bash, PowerShell, and Read commands. It supports intelligent color coding by identifying languages via file extension or content heuristics, and includes frontend rendering with zero token overhead, exit-code status display, and output collapsing. The plugin depends on `@deepseek-ai/schemastery`, allows configuring the default collapse state, and does not conflict with `dsh-better-tool-ui`.