Add auth domain workaround for same-site OAuth issue
- Add APP_URL config for main app domain
- Redirect login from status domain to auth domain
- After OAuth success, redirect back to status domain
- Use config values instead of hardcoding URLs
This works around the PDS rejecting same-site OAuth requests by using auth.zzstoatzz.com for OAuth flow while keeping status.zzstoatzz.io as the main app.