Add doctor Ollama coverage

[duyua9]

Summary\n- add focused check_ollama unit coverage for missing/non-Ollama configs\n- verify embedding and VLM Ollama api_base values are passed to the health check\n- cover the unreachable Ollama diagnostic path without requiring a real Ollama process\n\n## Validation\n- python3 -m py_compile tests/cli/test_doctor.py\n- PYTHONPATH=. uv run --no-project --with ruff python -m ruff check tests/cli/test_doctor.py\n- PYTHONPATH=. uv run --no-project --with pytest --with pytest-cov --with httpx --with pydantic --with pyyaml --with loguru --with rich --with json-repair python -m pytest --confcutdir=tests/cli tests/cli/test_doctor.py -k ollama

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