Each ChartTypePlugin now declares:
- display_name: human-readable label for the chart_type discriminator
  (e.g. "Line / Bar / Area / Scatter Chart", "Pivot Table")
- native_viz_types: dict mapping every Superset-internal viz_type the
  plugin produces to a user-friendly name
  (e.g. {"echarts_timeseries_line": "Line Chart", "echarts_area": "Area Chart"})

The registry gains display_name_for_viz_type(viz_type) which searches
all plugins' native_viz_types maps, replacing the need for a separate
viz_type_display_names.json or viz_type_names.py module.

ChartInfo gains a chart_type_display_name field populated via the registry,
so list_charts / get_chart_info return human-readable chart type names.
The MCP system instructions now reference display names rather than
internal viz_type identifiers.

H1: Delete 7 dead _pre_validate_* static methods from SchemaValidator
    — exact duplicates of plugin pre_validate() methods, never called
    after _pre_validate_chart_type() was updated to delegate to plugin.

H2: Inline DatasetValidator._normalize_xy_config/_normalize_table_config
    into XYChartPlugin/TableChartPlugin.normalize_column_refs() and delete
    both DatasetValidator helper methods. The 5 other plugins already
    called _get_canonical_column_name directly; XY and Table now match.

H3: Add generate_name()/resolve_viz_type() to ChartTypePlugin protocol
    and BaseChartPlugin, implement in all 7 plugins. Replace the 7-arm
    isinstance chain in generate_chart_name() and the 7-arm elif chain
    in _resolve_viz_type() with single-line registry dispatch.

H4: Add a sync comment above _CHART_TYPE_ERROR_HINTS to document that
    it must stay in sync with the plugin registry.

M4: Move logger=logging.getLogger(__name__) from inside
    XYChartPlugin.get_runtime_warnings() to module scope.

…xes, test repairs

On top of the dead-code elimination in the previous commit:
- Add lazy _ensure_plugins_loaded() bootstrap to ChartTypeRegistry so the
  registry is populated even without importing app.py (fixes isolated test runs)
- Delegate _RegistryProxy methods to module-level functions so bootstrap runs
- Guard register() against empty chart_type strings
- Add generate_name + resolve_viz_type to ChartTypePlugin Protocol and
  BaseChartPlugin; delegate generate_chart_name/_resolve_viz_type in
  chart_utils to the plugin registry
- Add _with_context static helper to BaseChartPlugin (shared by all plugins)
- Fix stale 'five methods' → 'eight methods' docstring in plugin.py
- Add TypeVar _C to normalize_column_names so mypy infers correct return type
- Fix broken tests: update _pre_validate_big_number_config → _pre_validate_chart_type,
  remove deleted TestNormalizeXYConfig/TestNormalizeTableConfig classes,
  update runtime validator tests for removed _validate_format_compatibility /
  _validate_cardinality methods, add x is not None narrowing guards

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…nal corrections, cardinality suggestions

- Remove redundant local imports from BigNumberChartPlugin.post_map_validate()
  now that BigNumberChartConfig and is_column_truly_temporal are at top level
- Add explanatory comments on the two remaining local get_registry imports in
  chart_utils.py and dataset_validator.py (circular import prevention)
- Fix schema_validator.py and generate_chart.py docstring: XY 'x' field is
  optional (defaults to dataset primary datetime column), not required
- Propagate cardinality suggestions alongside warnings in XYChartPlugin
- Clarify app.py instructions: chart_type_display_name is null for viz_types
  outside the 7 generate_chart-supported types

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

All per-method local imports in the 7 chart plugins were moved to module-level.
None of them create circular imports: schemas.py, chart_utils.py, and
dataset_validator.py are safe to import at plugin load time because those
modules guard their own registry lookups with local imports.

- big_number: add map_big_number_config, _big_number_chart_what,
  _summarize_filters, DatasetValidator to top-level imports
- pie: add map_pie_config, _pie_chart_what, _summarize_filters, PieChartConfig,
  DatasetValidator to top-level imports
- xy: add map_xy_config, _xy_chart_what/context, XYChartConfig, DatasetValidator,
  FormatTypeValidator, CardinalityValidator to top-level imports
- table: add map_table_config, _table_chart_what, _summarize_filters,
  TableChartConfig, DatasetValidator to top-level imports
- pivot_table: add map_pivot_table_config, _pivot_table_what, _summarize_filters,
  PivotTableChartConfig, DatasetValidator to top-level imports
- mixed_timeseries: add map_mixed_timeseries_config, _mixed_timeseries_what,
  _summarize_filters, MixedTimeseriesChartConfig, DatasetValidator to top-level
- handlebars: add map_handlebars_config, _handlebars_chart_what, _summarize_filters,
  HandlebarsChartConfig, DatasetValidator to top-level imports

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>