v1.3: Upgrade quality and efficiency

Changelog — v1.3

Added

• Reference-grounded gradient extraction — Gradients are now sampled directly from the reference image using band-median analysis, replacing manually guessed gradient stops. Also adds blue-collapse detection and magenta-lean hints for improved color fidelity.
• Candy-coat material model — Added support for dielectric candy/anodized/PVD-style finishes with tuned PBR parameters for richer, more accurate coatings. Includes automatic material classification (e.g. chrome → gem-metal, bright-clean → gemstone) and palette hue risk analysis.
• CIEDE2000 color metric — Introduced an accurate CIEDE2000 (ΔE00) implementation with sRGB → CIELAB conversion, validated against Sharma’s reference test pairs for perceptual color comparison.
• Divine Eye color diagnostics (report-only) — Added new analysis signals:
  • Hue Zone Parity detects hue shifts across gradient bands (e.g. purple drifting toward blue).
  • Specular Wash detects saturation loss and cyan drift caused by overly strong highlights.
    These metrics are currently informational only and do not affect validation scores while calibration is in progress.

Improved

• InstancedMesh rendering — Repeated geometry is now rendered using a single draw call for significantly better performance. Improved cluster resolution also eliminates previous base-geometry crashes.
• Ground blade UV mapping — UV generation now uses the true Y-span of the geometry, fixing edge clamping artifacts that previously caused flat colors and white tip issues.
• Cutout generation — Extrusion now supports Shape.holes and oval loop cutouts, enabling clean wire-cutter style holes without requiring CSG operations.