rendering: add DrawList picking and selection

[tritao]

Summary

Rebuild the retained DrawList picking and selection layer on frozen #50.

This layer provides:

• backend-neutral command paths and structured object/face/edge/vertex ranges;
• frame-local pick lookup tables with exact integer IDs;
• an explicit core-profile R32UI ID-buffer update and radius query;
• picking coverage that reuses the frozen raster, line, point, triangle-fallback, and pixel geometry;
• explicit selection and highlight targets rendered as depth-tested blended overlays;
• no manager, application identity, interaction policy, or stage/layer ownership.

Ordinary visual rendering does not perform picking work implicitly.

Stack

Layer 16/18, based on PR #50.