#751 call_llm implements only Ollama; Anthropic/OpenAI raise NotImplementedError (blocks Claude)

engine/tools/llm/core/providers.py:87-112 _call_anthropic/_call_openai/etc raise NotImplementedError; stubs take only prompt (no messages/tools). Highway Agents needs Claude => implement Anthropic Messages API provider (multi-turn + tools/tool_choice, same return shape). Until then Phase 0 is Ollama-only.