Standardize filter output figures across MOSuite function calls

[phoman14]

Summary

This PR aligns the filter-counts capsule with the package-level figure standardization work. The intent is for figures produced from this capsule to match figures produced by the corresponding MOSuite function calls, rather than carrying capsule-specific color or legend defaults.

Changes

• Use the same default plot color palette as the MOSuite package for filter-counts outputs.
• Leave the histogram legend font size blank by default so filter_counts() can use the package's automatic legend text scaling for many or long labels.
• Parse an explicit histogram legend font size only when the user provides one.
• Keep the capsule parameter descriptions focused on the user-facing defaults.
• Update CHANGELOG.md for the user-facing default changes.

Validation: local capsule tests passed (PASS 7).

Issues

No linked issue.

PR Checklist

(Strikethrough any points that are not applicable.)

• This comment contains a description of changes with justifications, with any relevant issues linked.
• Run the capsule in Code Ocean and ensure it completes successfully with no errors. Local capsule tests passed.
• Update CHANGELOG.md with a short description of any user-facing changes and reference the PR number. Follow the style described in https://style.tidyverse.org/news.html
• The tests workflow succeeds on the latest commit.