Initial release of the DSH side-chat plugin.
- /side opens an independent read-only side chat that inherits the main session's context, persona, and model
- Context copied as agent memory but not displayed in the panel
- Read-only tool whitelist (no bash/write/edit)
- Markdown rendering (tables, code blocks, headings, lists)
- Adaptive panel: real layout sidebar (wide) / overlay drawer (narrow)
- Close fully disposes the agent