Improve package functions and documentation

[JustSplash8501]

Summary

• Keep the private Shiny application, deployment metadata, web assets, and secrets outside the R package and GitHub build context.
• Add the hosted MeatColor Lab Explorer teaching link to the README.
• Add tidyverse-friendly CIELAB hue and chroma functions.
• Add selected-wavelength and calibrated K/S myoglobin calculations.
• Configure and pin roxygen2, generated documentation, contributor guidance, and documentation-drift CI.
• Strengthen finite-value and reflectance-scale validation.
• Expand tests, package documentation, NEWS, and the introductory vignette.

Why

This keeps the repository focused on its public R-package purpose while making the package APIs easier and safer to use for meat-color analysis. It also makes documentation generation reproducible and prevents invalid scientific inputs from silently producing results.

Validation

• 196 test expectations pass.
• Roxygen generation is idempotent.
• A clean source build succeeds.
• R CMD check without the PDF manual completes with Status: OK.
• Examples and vignettes build successfully.