DEV: Surface topic_id in errors of summarization backfill

[keegangeorge]

This update ensures that the topic_id related to the error when summarizing is surfaced in the logs, which should help track down the reason for the errors.

i.e.

Error summarizing topic 245: DiscourseAi::Completions::Endpoints::Base::CompletionFailed - {
    "error": { 
        ...