Group charts — bertopic pooled

• bertopic_pooled from aggregate_bertopic_group, after a group-level BERTopic refit on merged preprocessed source segments from all transcripts (not joined transcript topic IDs).

• Chart: group.bertopic.pooled.topic_share.global — bar of document-topic shares for non-outlier topics.

• Fail closed without non-outlier topics / when all_outlier is true (emit no chart specification).

• Aggregation registry: agg_id=bertopic, selector=any_of(["bertopic"]), deps=[].