Perplexity's /rest/models/config now exposes claude50sonnet and claude50sonnetthinking. Add both to KNOWN_MODELS with the official labels from the config. The stream's display_model can report "turbo" even when the requested model was honored, so prefer user_selected_model when present and not "turbo" so tool metadata reflects the model actually used. Closes #7 Co-authored-by: Ivan Pereira <183991+ivanrvpereira@users.noreply.github.com>