feat: add used-car module and fix API response handling

- Add used-car pages: list, detail, create, edit, mine
- Add CarCard and PriceModal components
- Fix API response interceptor to accept both code 200 and 0
- Fix detail page: was incorrectly using edit page template
- Fix edit page: remove res.code check after API call
- Add image URL processing (localhost → localhost:8787)
- Add i18n translations for used-car module in 5 languages

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

frontend/vite.config.ts

@@ -26,6 +26,10 @@ export default defineConfig({
         target: 'http://127.0.0.1:8787',
         changeOrigin: true,
       },
+      '/uploads': {
+        target: 'http://127.0.0.1:8787',
+        changeOrigin: true,
+      },
     },
   },
   build: {