fix: use configured backend_url for API base instead of /api path

- Read HF_BACKEND_BASE_URL from localStorage in api client
- Refresh baseURL on each request interceptor
- Persist backend_url from wizard config during app bootstrap
- Persist backend_base_url after setup save

src/pages/SetupWizardPage.tsx

@@ -92,6 +92,10 @@ export default function SetupWizardPage({ wizardBase, onComplete }: Props) {
         headers: { 'Content-Type': 'application/json' },
       })
 
+      if (form.backend_base_url) {
+        localStorage.setItem('HF_BACKEND_BASE_URL', form.backend_base_url)
+      }
+
       setStep(4)
     } catch (err: any) {
       setError(`保存配置失败: ${err.message}`)