This PR adds the ability to set the thinking effort of a model. Right now this only applies to Opus 4.6 through the Zed provider. This is gated behind the `cloud-thinking-toggle` feature flag. UI is still rough; needs a design pass: <img width="639" height="163" alt="Screenshot 2026-02-05 at 7 45 54 PM" src="https://github.com/user-attachments/assets/2b5a9ef8-74cd-498e-9c81-b92666572409" /> <img width="263" height="148" alt="Screenshot 2026-02-05 at 7 45 58 PM" src="https://github.com/user-attachments/assets/40232cb0-1743-443b-b04c-5cd33065513d" /> Release Notes: - N/A