feat(cli): simplify top bar — title + host only

- Show 'Mosaic Stack TUI' on left, gateway host on right
- Remove connection status from top bar (lives in footer)
- Remove model/conversation from top bar (lives in footer)

packages/cli/src/tui/app.tsx

@@ -31,13 +31,7 @@ export function TuiApp({ gatewayUrl, conversationId, sessionCookie }: TuiAppProp
 
   return (
     <Box flexDirection="column" height="100%">
-      <TopBar
-        connected={socket.connected}
-        connecting={socket.connecting}
-        gatewayUrl={gatewayUrl}
-        conversationId={socket.conversationId}
-        modelName={socket.modelName}
-      />
+      <TopBar gatewayUrl={gatewayUrl} />
 
       <MessageList
         messages={socket.messages}