Add chart renderer registry and mechanical Vega renderer

ID	DFT_CORE-ADD_CHART_RENDERER_REGISTRY_AND_MECHANICAL_VEGA_RENDERER
Status	completed
Priority	p1
Milestone	m1-ft-analytics-analyst-pilot
Owner	sr-engineer-architect

Problem

Introduce renderer-family dispatch, rebuild standard Vega-Lite translation around resolved chart semantics, and make layered chart rendering explicit.

Context

Possible Solutions

Plan

Implementation Progress

Review Feedback

[ ] Review cleared