Function resolve_citekey

pub fn resolve_citekey(
    ctx: &ServerContext,
    citekey: &str,
) -> Result<String, String>

Resolve a citekey to a Zotero item key.

Uses the DbPool’s multi-source resolution:

1. zotero.sqlite citationKey field (99.9% coverage)
2. better-bibtex.migrated fallback