Delete a knowledge base

Reference data for building an agent — every id an Agent's primary_language_id/default_voice_id/llm_server_id/asr_model_id/ knowledge_base_id must be one of. There is no fixed enum for these: call GET /meta first and use the ids it returns, since voices, languages and models are added over time. NOTE the camelCase keys on three of the six lists — they are named for the dashboard store that consumes them, and renaming them would break it.