Conversation
Top-level chat screen: conversation message list + input + chat top bar (with its 3-dot menu) + an optional feedback bottom sheet overlay. This is the composable that the navigation host actually renders for the conversation route.
Owns indexes 0 (Settings) and 1 (Cancel chat) of its top-bar menu; everything after that is delegated to HandleLocalDevMenuItem so the labels and handlers stay in lock-step with MainScreen's parallel menu.