fix: Add cho parameter to search_cars for import car search

- Added 'cho': '' parameter to enable searching both domestic and import cars
- This fixes Toyota Prius (and other import cars) not appearing in search results

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/api/carmodoo.py

@@ -200,6 +200,7 @@ class CarmodooClient:
                 form_data = {
                     'sf_page': str(page - 1),  # 0-based
                     'sf_pageSize': str(page_size),
+                    'cho': '',  # 국산/수입 구분 (빈값이면 전체 - 수입차 검색을 위해 필수)
                 }
 
                 if maker_code: