Fix effort and provider handling in thread turn start

- Only include `effort` in start command when a value is selected
- Persist effort selection via composer draft state and hide picker when unavailable
- Add optional `provider` to `ClientThreadTurnStartCommand`
- Simplify thread model fallback selection in `ChatView`
43b64bf17dJulius Marminge committed on 3/6/2026, 2:13:19 AMparent4f47f33
2 files changedLine totals unavailable