Default weight applied to KG matches when boosting a chunk’s relevance score.
A weight of 1.0 means a chunk whose path and content fully match the top KG concept
can roughly double its rank vs an unmatched chunk with the same base score.
Apply KG boost to a batch of chunks and sort by boosted score (descending).
Mutates relevance_score in place so downstream consumers can see the boost reflected
in the JSON output – otherwise the ordering would be inexplicable.