feat: label AI-generated conversation messages

tests/conversation-automation.test.ts

@@ -46,6 +46,7 @@ describe('conversation automation', () => {
     expect(third).toMatchObject({ kind: 'human-required', remainingTurns: 0 });
     expect(chat.sendChatMessage).toHaveBeenCalledTimes(3);
     expect(getSaved()?.automation).toMatchObject({ turnsUsed: 3, status: 'human-required' });
+    expect(getSaved()?.automation.aiMessageFingerprints).toHaveLength(3);
     expect(await service.processConversation(incoming(3))).toBeNull();
   });