Subject: Anky needs to talk back — two changes to the API

The app has a working writing flow now. User writes, session ends, writing gets submitted to POST /write. But Anky's responses are hardcoded on the client. We need the backend to actually respond.

Change 1: Add fields to POST /write response — ankyResponse, nextPrompt, mood. Generated by Claude with Honcho peer context. Must reference something specific from the writing, not generic encouragement.

Change 2: New endpoint GET /swift/v2/chat/prompt — called on app launch, returns Anky's opening message. First-ever user: "tell me who you are." Returning user: Honcho-powered prompt that picks up where they left off.