refactor: refine enter/space key preventDefault logic

Separate isCombobox check and apply different preventDefault logic:
- Space: prevent only when not editable
- Enter: prevent only when not combobox

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: zombieJ

src/BaseSelect/index.tsx

@@ -471,8 +471,9 @@ const BaseSelect = React.forwardRef<BaseSelectRef, BaseSelectProps>((props, ref)
     // Enter or Space opens dropdown (ARIA combobox: spacebar should open)
     if (isEnterKey || isSpaceKey) {
       // Do not submit form when type in the input; prevent Space from scrolling page
-      const isEditable = mode === 'combobox' || showSearch;
-      if (!isEditable) {
+      const isCombobox = mode === 'combobox';
+      const isEditable = isCombobox || showSearch;
+      if ((isSpaceKey && !isEditable) || (isEnterKey && !isCombobox)) {
         event.preventDefault();
       }