enhance(citation): render citations server-side (#39373)

Replace citation-js with a Go port of ruby-cff, which GitHub uses for
"Cite this repository", rendering APA and BibTeX server-side and
dropping about 770KB of JS. Output matches GitHub on 1568 of 1571
real-world files, the rest are improvements over GitHub.

- `CITATION.cff` wins over `CITATION.bib`, matched case-insensitively
and through symlinks
- `CITATION.bib` is offered as-is, without APA

Signed-off-by: silverwind <me@silverwind.io>

web_src/js/globals.d.ts

@@ -31,7 +31,6 @@ interface Window {
         SortType: string,
         StatusFilterMap: Record<string, string>,
       },
-      citationFileContent?: string,
       prReview?: {
         numberOfFiles: number,
         numberOfViewedFiles: number,