fix(cli): prevent autocomplete UI flicker by decoupling disabled state reset from completion refresh

When typing outside of shell mode (e.g., using `@` completion), the `useShellCompletion` hook was continuously re-rendering and executing its `useEffect` because `performCompletion` was recreated on every keystroke (since its `query` dependency changed).

Because `enabled` was false, the effect unconditionally called `setSuggestions([])`, rapidly overriding the suggestions populated by `useAtCompletion` and causing severe UI flickering.

This splits the effect to ensure `setSuggestions([])` is only called once when `enabled` becomes false, stabilizing the suggestions list.

packages/cli/src/ui/hooks/useShellCompletion.ts

@@ -497,13 +497,16 @@ export function useShellCompletion({
     setIsLoadingSuggestions,
   ]);
 
-  // Debounced effect to trigger completion
   useEffect(() => {
     if (!enabled) {
       setSuggestions([]);
       setIsLoadingSuggestions(false);
-      return;
     }
+  }, [enabled, setSuggestions, setIsLoadingSuggestions]);
+
+  // Debounced effect to trigger completion
+  useEffect(() => {
+    if (!enabled) return;
 
     if (debounceRef.current) {
       clearTimeout(debounceRef.current);
@@ -519,7 +522,7 @@ export function useShellCompletion({
         clearTimeout(debounceRef.current);
       }
     };
-  }, [enabled, performCompletion, setSuggestions, setIsLoadingSuggestions]);
+  }, [enabled, performCompletion]);
 
   // Cleanup on unmount
   useEffect(