We’re adding threaded conversations to our documents and tasks. Please build a backend that lets users post new comments and reply to existing ones, and returns the full nested discussion for a document in a single request. All actions must be tied to the signed-in user via an OAuth2 bearer token. Implement a REST API with Fastify (Node.js) and PostgreSQL: use a self-referencing schema (parent_comment_id) and a recursive CTE to assemble the complete comment tree. Provide endpoints to create a comment and to fetch the structured thread for a given document.