Searches the local DuckDB cache using full-text search (BM25 ranking) across
comic titles, alt text, and transcripts. Results are ranked by relevance.
Supports stemming (e.g., "running" matches "run") and stopword removal.
Run updateConfig() first to populate the database and build the search index.
Value
A data frame containing matching XKCD comics with columns num, date,
title, alt, and score (BM25 relevance), ordered by relevance.
If no matches are found, an empty data frame is returned invisibly, and a message is printed.
The function will stop with an error if the local database or search index is not found.