fix: create example log directory correctly

[haosenwang1018]

Summary

• create the actual example log directory instead of its parent in configure_logging()
• add a focused regression test covering nested LOG_DIR values
• keep the fix scoped to the current mainline example file that replaced the older OpenAI demo path

Testing

• uv run python -m pytest tests/test_raganything_example.py -q
• uv run ruff check examples/raganything_example.py tests/test_raganything_example.py
• uv run ruff format --check examples/raganything_example.py tests/test_raganything_example.py
• git diff --check

[LarFii]

Thanks for your contribution!