fix: use window.open for mobile links (#217)

## Change Summary

Follow up to #200. Add changeset, use `window.open` in `SignInButton`.

## Merge Checklist

_Choose all relevant options below by adding an `x` now or at any time
before submitting for review_

- [x] PR title adheres to the [conventional
commits](https://www.conventionalcommits.org/en/v1.0.0/) standard
- [x] PR has a changeset
- [x] PR has been tagged with a change label(s) (i.e. documentation,
feature, bugfix, or chore)
- [ ] PR includes documentation if necessary
- [x] All commits have been signed

.changeset/mean-baboons-collect.md

@@ -0,0 +1,5 @@
+---
+"@farcaster/auth-kit": patch
+---
+
+fix: use window.open for mobile links

packages/auth-kit/src/components/SignInButton/SignInButton.tsx

@@ -81,7 +81,7 @@ export function SignInButton({
     setShowDialog(true);
     signIn();
     if (url && isMobile()) {
-      window.location.href = url;
+      window.open(url, "_blank");
     }
   }, [isError, reconnect, signIn, url]);