Tidymodels Skills 0.5.0

Added

• Plugin manifest (.claude-plugin/plugin.json) for the tidymodels-skills plugin.
• Grading configuration for the add-recipe-step skill evals.

Changed

• Updated parsnip skills (add-parsnip-model, add-parsnip-engine) for parsnip 1.5.0.
• Updated quantile guidance to reflect the latest version of parsnip.
• Updated recipes skill script references to match the latest CRAN release.
• Updated yardstick skill file references after script renaming in its latest release.
• Updated dials skill references for the consolidated grid source files
  (R/grids.R, R/space_filling.R, R/extract.R) and refreshed the
  values_weight_func example (cos/inv, now 9 values).
• Refreshed roxygen2 documentation.
• Reorganized the repository structure.
• Improved the evaluation script and updated eval R paths and configs.
• Added guards to prevent unintended git commit usage.

Fixed

• Fixed a roxygen issue in the parsnip grader.
• Replaced dead documentation links with nearest live matches.