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/App.tsx

@@ -33,7 +33,11 @@ export default function App() {
       const res = await axios.get(`${WIZARD_BASE}/api/v1/config/harborforge.json`, {
         timeout: 5000,
       })
-      if (res.data && res.data.initialized === true) {
+      const cfg = res.data || {}
+      if (cfg.backend_url) {
+        localStorage.setItem('HF_BACKEND_BASE_URL', cfg.backend_url)
+      }
+      if (cfg.initialized === true) {
         setAppState('ready')
       } else {
         setAppState('setup')