Add iterative palette proof calibration

[vycdev]

Summary

• add configurable, printable palette-proof 3MF exports with immutable job metadata, saved evaluations, deletion, re-downloads, and grouped follow-up rounds
• persist validated appearance evidence in filament profiles and use a deterministic held-out-gated Lab correction for auto-paint scoring and simulated previews
• document the palette-proof workflow and add regression coverage for proof selection, geometry, exports, persistence, fitting, and optimizer integration

Why

Kromacut previously had no closed feedback loop between physical palette-proof prints and its simulated colors. This workflow lets users record what actually printed closest to each target and safely use sufficiently strong evidence to improve later auto-paint results without changing filament assignments, hiding-distance calibration, or export colors.

Impact

Users can generate proof sheets, record closest/tied/no-match results, continue testing the same targets, or rotate to new targets. Appearance correction is applied only when training and held-out evidence clear strict quality gates.

Validation

• npm test ? 367 passing
• npm run build ? passing (Vite reports the existing large-chunk warning)
• npm run lint ? passing
• git diff --check develop...HEAD ? passing