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

Collapse multi-file plugin into single index.tsx. Polygon keeps its
custom buildQuery (line_column required, optional metric/elevation
metric handling, null filter) and transformProps (json/geohash/zipcode
polygon decoders, fixed/metric elevation, reverse_long_lat). Largest
deckgl layer (500+ lines) but follows the same pattern. Polygon.tsx
component stays as sibling for Multi.

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