* FEATURE: Inline topic summary. Cached version accessible to everyone.
Anons and non-members of the `custom_summarization_allowed_groups_map` groups can see cached summaries for any accessible topic. After the first 12 hours and if the posts to summarize have changed, allowed users clicking on the button will automatically re-generate it.
* Ensure chat summaries work and prevent model hallucinations when there are no messages.
* DEV: Document external topic id endpoints
This commit documents the existing Create Topic endpoint with the
`external_id` param and documents the new get topic by external id
endpoint.
It also refactors the existing topic show endpoint to use the new format
where we load the expected json schema response from a file.
See: 71f7f7ed49
* clean up unused test variables
