Introduces luminos_lib/capabilities.py as the single source of truth for
optional package availability. Detects anthropic, tree-sitter, python-magic
and their grammar packages. Provides check_ai_dependencies() for gating
--ai mode and print_status() for --install-extras. Also hosts clear_cache()
to avoid pulling heavy AI imports for cache cleanup.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
