Add --no-tools flag that allows starting pi without any built-in tools,
enabling extension-only tool setups (e.g., pi-ssh-remote).
- Add --no-tools flag to CLI args parsing
- Handle --tools '' (empty string) as equivalent to no tools
- Fix system prompt to not show READ-ONLY mode when no tools (extensions may provide write capabilities)
- Add tests for new flag and system prompt behavior
fixes#555
Carlos Villela