⚡ perf(search): add 100ms debounce to search suggestions

- Add setTimeout with 100ms delay to reduce API calls
- Add cleanup function to clear timer on unmount

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/components/SearchBox.tsx

@@ -78,8 +78,9 @@ const SearchBox: React.FC<SearchBoxProps> = ({
     return () => document.removeEventListener('mousedown', handleClickOutside);
   }, []);
 
-  // Fetch suggestions immediately without debounce
+  // Fetch suggestions with 100ms debounce
   useEffect(() => {
+    const timer = setTimeout(() => {
       if (query.trim()) {
         fetchSuggestions(selectedEngine.name, query).then(results => {
           // Only update if results are different to avoid unnecessary re-renders
@@ -99,6 +100,9 @@ const SearchBox: React.FC<SearchBoxProps> = ({
         setShowSuggestions(false);
         setSelectedIndex(-1);
       }
+    }, 100);
+
+    return () => clearTimeout(timer);
   }, [query, selectedEngine.name]);
 
   const performSearch = useCallback((text: string) => {