Allow selecting the model for title generation in the config

From what I understand, the system currently uses getSmallModel for generating titles, which with OpenRouter selects Claude 3.5 Haiku in my case. However, since my balance is empty and I'm using moonshotai/kimi-k2:free instead, the session won't start.

there's already a config in small_model i believe

Thanks, I didn't find this in the documentation.