docs: restructure and update research literature page

[magnus-madsen]

Reworks research-literature.md, which was a flat list of ten bare titles with no authors, venue, or year, and had not been updated since 2022.

Presentation

Adopts the same entry format as videos.md — bold linked title, then authors, venue, and year in italics:

- **[The Principles of the Flix Programming Language](https://dl.acm.org/doi/10.1145/3563835.3567661)**\
  *Magnus Madsen @ Onward! 2022*

Papers are grouped into Language Design, Types and Effects, Datalog and Fixpoints, and Compilation, reverse-chronological within each section.

Content

• Adds the nine papers published since 2022: Language-Integrated Datalog, Qualified Types with Boolean Algebras, Overloading the Dot, Associated Effects, With or Without You, Fast and Efficient Boolean Unification, Restrictable Variants, Purity Reflection, and Breaking the Negative Cycle. The book already linked talks for two of these in videos.md but not the papers themselves.
• Notes the Distinguished Paper Award (Purity Reflection) and Distinguished Artifact (Language-Integrated Datalog).
• Cross-links the five papers that have a corresponding chapter.
• Adds a note that Flix has evolved since many of these papers were published.
• Moves the page last under Additional Information in SUMMARY.md, and reorders additional-information.md to match. That prose list was also missing Videos, so it is now added.

Verification

• All 18 DOIs resolve through doi.org; both direct PDF links return 200.
• Every title, author list, author order, venue, and year was checked against https://cs.au.dk/~magnusm/. The three ECOOP LIPIcs numbers were each confirmed against Dagstuhl to match the right paper.
• The TAPAS 2016 entry is not on the homepage; its authors were confirmed from the abstract PDF.
• mdbook build succeeds and all internal links resolve.

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