fix(tui): address copilot round 3 on #14145

- appLayout.tsx: restore the 1-row placeholder when `showStickyPrompt`
  is false. Dropping it saved a row but the composer height shifted by
  one as the prompt appeared/disappeared, jumping the input vertically
  on scroll.
- useInputHandlers: gateway.rpc (from useMainApp) already catches errors
  with its own sys() message and resolves to null. The previous `.catch`
  was dead code and on RPC failures the user saw both 'error: ...' (from
  rpc) and 'failed to toggle yolo'. Drop the catch and gate 'failed to
  toggle yolo' on a non-null response so null (= rpc already spoke)
  stays silent.

ui-tui/src/components/appLayout.tsx

@@ -173,12 +173,14 @@ const ComposerPane = memo(function ComposerPane({
         </Text>
       )}
 
-      {status.showStickyPrompt && (
+      {status.showStickyPrompt ? (
         <Text color={ui.theme.color.dim} wrap="truncate-end">
           <Text color={ui.theme.color.label}>↳ </Text>
 
           {status.stickyPrompt}
         </Text>
+      ) : (
+        <Text> </Text>
       )}
 
       <StatusRulePane at="top" composer={composer} status={status} />