Add guidance on when to use articles over vignettes

[Copilot]

Extends the "Vignettes vs Articles" section with specific use cases for choosing articles from the R Packages book.

Changes

• New subsection: "Additional considerations for choosing articles over vignettes" in code-repositories/package-structure.qmd
• Four key scenarios where articles are preferred:
  • Code requiring authentication or external services (shouldn't execute on CRAN)
  • Demonstrating integration with non-dependency packages
  • Graphics-heavy content that would exceed CRAN size limits
  • Trade-off: reduced accessibility for offline users
• Citation: [@wickham2023rpkgs, Section 17.4.1] using existing bibliography entry

The addition provides actionable criteria for developers deciding between vignette and article placement.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>summarize and link to https://r-pkgs.org/vignettes.html#sec-vignettes-article</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes summarize and link to https://r-pkgs.org/vignettes.html#sec-vignettes-article #196

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