fix: remove hardcoded API token from SettingsScreen

- Replace hardcoded Bearer token default with empty string
- Remove auto-save in useEffect that wrote defaults to SecureStore
  without user consent on first app launch

Fixes #2

src/screens/SettingsScreen.tsx

@@ -28,7 +28,7 @@ export async function getApiConfig(): Promise<ApiConfig | null> {
 
 export default function SettingsScreen() {
   const [url, setUrl] = useState('https://weegschaal.eddydevink.nl')
-  const [token, setToken] = useState('REDACTED')
+  const [token, setToken] = useState('')
   const [showToken, setShowToken] = useState(false)
   const [syncing, setSyncing] = useState(false)
 
@@ -37,8 +37,6 @@ export default function SettingsScreen() {
       if (c) {
         setUrl(c.url)
         setToken(c.token)
-      } else {
-        saveConfig({ url, token })
       }
     })
   }, [])