openai/gpt-chat-latest → B (3:2)

Side B fixes a functional data-model bug by importing Reddit listing children directly under the parent without path expansion (`apply_entity_under_parent` replacing `link_child` behavior), updates the ranking panel to display imported child titles via tree lookups, and strengthens integration tests to cover SSE morphs and children fetches. Side A usefully centralizes base URL generation around `HOSTNAME`/current origin and adjusts staging deployment, but much of the patch is refactoring existing URL logic rather than introducing new application behavior.