- Updates create_chart logic to automatically remove x_axis from groupby for ECharts timeseries charts, preventing duplicate dimension usage.
- Updates and expands unit test to verify x_axis is excluded from groupby, using improved test mocks for accurate backend simulation.
- Updates documentation (README.md, README_ARCHITECTURE.md, README_PHASE1_STATUS.md, README_SCHEMAS.md) to clarify create_chart tool behavior and schema, including new groupby/x_axis handling.
- No breaking changes to tool signatures; behavior is now more robust and LLM-friendly.