feat(ui): persist AI responses after interrupt

[andrewrisse]

AI responses after interrupt

Type: Feature

Description: If you interrupt an AI response and leave the conversation (for example by switching to a new thread), but you come back to the conversation, the AI response (that was incompleted) is lost. It should be persisted. This is not a bug, it's new functionality.

Note - this story is dependent on the team accepting Supabase as our solution per the ADR. #293

User Story:
As a mission hero using LeapfrogAI UI, I want to see the last response from the AI even if it was interrupted so that I am not confused that I went to the wrong thread where I thought I had asked a question.

Acceptance Criteria:

• Partial responses are saved.
• Unit and/or E2E tests. This may be more easy and practical to test with just an E2E.

[andrewrisse]

Closed with issue #15 in lfaiui repo