fix: return an error for non-2xx responses using error_for_status()

Previously, the request function returned Ok(()) even if the
HTTP response status was an error (4xx/5xx). By adding
`response.error_for_status()?`, we correctly propagate
HTTP errors rather than masking them, ensuring that timeouts and
other non-2xx status codes produce an error as expected.

pubky/src/shared/auth.rs

@@ -143,11 +143,13 @@ impl PubkyClient {
         path_segments.push(&channel_id);
         drop(path_segments);
 
-        self.request(Method::POST, callback)
+        let response = self.request(Method::POST, callback)
             .body(encrypted_token)
             .send()
             .await?;
 
+        response.error_for_status()?;
+
         Ok(())
     }