Clean up R CMD check --as-cran for the 0.1.0 release

[sbfnk-bot]

Description

Gets R CMD check --as-cran fully clean ahead of the first CRAN release, and bumps the version to 0.1.0.

Fixes the one warning and four notes from the check:

• Rd argument warnings: removed the method-only max_value/width/cdf_cutoff @param tags from the discrete_pmf generic (folded into ...); added ignore_uncertainty to the mean.dist_spec signature so the documented arg appears in \usage; documented new_dist_spec's distribution argument.
• Hidden / non-standard files: added a .Rbuildignore (there was none), covering .github, .lintr, .claude, CITATION.cff, README.Rmd, _pkgdown.yml, codecov.yml, LICENSE.md, etc.
• Undefined globals: added @importFrom methods is and @importFrom utils tail, and methods to Imports.
• NEWS: added a # distspec 0.1.0 heading so the news entries parse.

Also adds cran-comments.md. Local R CMD check --as-cran is now 0 errors, 0 warnings, 0 notes (CRAN will still add the expected "New submission" note). 225 tests pass, 0 lints.

No linked issue — CRAN-release prep. The actual submission is left to the maintainer.

Initial submission checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have tested my changes locally (using devtools::test() and devtools::check()).
• I have added or updated unit tests where necessary.
• I have updated the documentation if required and rebuilt docs if yes (using devtools::document()).
• I have followed the established coding standards (and checked using lintr::lint_package()).
• I have added a news item linked to this PR.