feat(website, backend): Sequence citations

[tombch]

Summary

Backend Changes

• Adds a get-sequence-cited-by-publication endpoint, which returns citing sources for seqsets that include the sequence entry.
• The endpoint (currently) requires an accession and version for the sequence entry. With these, it returns citing sources for seqsets that either include the exact {accession}.{version} that was queried, or include an unversioned {accession} for the sequence.

Website Changes

• Updates the SeqSetCitationsList component to a more generic CitationsList component, and adds a modal to the sequence details page viewable with a View Citations button. The citations displayed also include the seqset they came from, and how the sequence was used (i.e. pinned version or unversioned).

Screenshot

PR Checklist

• All necessary documentation has been adapted.
• The implemented feature is covered by appropriate, automated tests.
• Any manual testing that has been done is documented (i.e. what exactly was tested?)

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[claude]

This PR may be related to: #990 (Unit test citations logic), #1501 (Check Crossref via API to see what papers citing DOIs)

[theosanderson]

(haven't seen a preview or anything but just trying to give some early feedback: IMO we could surface some of these even without opening a modal, in the main page)