- Add Drawing.HasCustomColor, set when a color is picked in Drawing
Properties or comes from a library record with a stored color.
- Persist it as customColor in .nest files (omitted when false) and keep it
out of drawing packages; split pieces inherit it.
- Recolor non-custom drawings from the active palette when a nest opens and
when the scheme changes; custom colors keep their palette slot.
- Library settings store a color only when it is custom.
- Document drawing colors in nest-file-format.md and nesting-view-colors.md.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>