feat(glyph): consolidate plugin-chart-point-cluster-map to defineChart()

Fold the legacy multi-file plugin (index.ts + controlPanel.ts +
transformProps.ts + buildQuery.ts) into a single src/index.tsx using
defineChart(). MapLibre.tsx component and helpers stay separate.

- arguments: {} (legacy chart, all controls inline via prependSections)
- suppressQuerySection: true (own Query section)
- additionalControlOverrides: groupby description preserved
- formDataOverrides: getStandardizedControls().popAllColumns() preserved

41 plugin tests still pass.

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