Add mapgl composition helpers

[NewGraphEnvironment]

Problem

Same composition boilerplate from gq#14 applies to mapgl interactive maps. Standard basemap config, navigation controls, and popup templates are duplicated across projects.

Proposed Solution

Function	Purpose
gq_mapgl_basemap()	Standard tile source configuration
gq_mapgl_controls()	Navigation, scale bar, layer toggle
gq_mapgl_popup()	Standard popup template from column names

Build after tmap composition helpers land — same data, same registry, interactive counterpart.