Fixes reference-based preview fields causing groq2024 search failures

Fixes "Reference search failed: score() function received unexpected expression" when searching with the groq2024 search strategy. Searches involving document types whose preview select traverses a reference (e.g., subtitle: 'author.name') no longer fail.

Note that these reference-traversed preview fields do not contribute to search matching or ranking under groq2024 (matching pre-5.31.0 behavior); they remain searchable under the default groqLegacy strategy.