New onboarding screen: <img width="1027" height="700" alt="Screenshot 2025-10-05 at 10 38 57 PM" src="https://github.com/user-attachments/assets/5dc49e53-68e7-4559-8ce0-1bada629781d" /> This PR also adds a new telemetry event: `Welcome Start Building Clicked` Release Notes: - N/A