feat(glyph): consolidate deckgl Heatmap layer to defineChart()

Collapse multi-file plugin into single index.tsx. Heatmap uses shared
buildSpatialQuery/transformSpatialProps, plus intensity/radius_pixels
controls and a linear color scheme palette. Heatmap.tsx component
stays as sibling for Multi.

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