acp: Add onboarding modal & title bar banner (#36784)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/agent_ui/src/ui.rs

@@ -1,3 +1,4 @@
+mod acp_onboarding_modal;
 mod agent_notification;
 mod burn_mode_tooltip;
 mod context_pill;
@@ -6,6 +7,7 @@ mod onboarding_modal;
 pub mod preview;
 mod unavailable_editing_tooltip;
 
+pub use acp_onboarding_modal::*;
 pub use agent_notification::*;
 pub use burn_mode_tooltip::*;
 pub use context_pill::*;