- @ file references with glob/dir support and size limits
- ! shell commands with timeout and output truncation
- inline permission dialog for destructive tool calls
- diff and artifact renderers with theme-aware highlighting

Tests: 40 client tests passing

- Add CommandPaletteScreen modal with fuzzy filtering and keyboard navigation.

- Bind Ctrl+P to push the palette; selected commands execute via registry.

- Make MarkdownRenderer theme-aware: headings, inline code, links, and code blocks use gnexus palette.

- Pick dracula/github-light code theme based on active theme brightness.

Co-Authored-By: Claude <noreply@anthropic.com>