feat(api): return more annotation details

[andrewrisse]

User Story

As the LeapfrogAI UI
I want to display the passage a RAG response used
So that users have more context on how the response was generated

Acceptance Criteria

Given a run returns a message with annotations
When the UI consumes that data
Then it has data for the file_citation IAW the OpenAI spec

Reference the OpenAI message object and ensure all fields for file_citation are being returned (content.text.annotations[0].file_citation).