Dataset documentation: roxygen docs for all exported data objects

[dlebauer]

Goal

• Ensure each exported dataset is documented and discoverable in R help.

Tasks

• For each exported data object (traitsview + support tables):
  • create an R/<name>.R file containing roxygen2 @docType data documentation
  • include: title, description, source, variables (key columns), and examples
• Ensure docs build cleanly with devtools::document().

Acceptance criteria

• ?traitsview works and describes the dataset clearly.
• help(package = "betydata") lists the datasets.
• R CMD check passes without undocumented objects.

Non-goals

• No extra wrapper functions or complex APIs.