Deduplicate geo chart rendering and config ownership

Problem

The geo rendering code still duplicates point-map and layered-point-map behavior across geo source resolution, projection selection, encoding assembly, tooltip generation, and visual defaults. Remaining hardcoded values also weaken the design principle that config is the single source of truth. Consolidate shared geo helpers and move the remaining map-specific visual defaults into config-backed settings without changing output behavior.

Context

Possible Solutions

Plan

Implementation Progress

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