Better Auth 1.3

Better Auth 1.3 introduces significant authentication enhancements including SAML 2.0 support in the SSO plugin, stable OIDC and MCP plugins with production-ready features, and a new Sign-In with Ethereum (SIWE) plugin. The release adds multi-team organization support, additional social providers (Notion, Slack, Linear, Faceit), and improved OAuth functionality. Key improvements include Zod 4 migration for better performance, enhanced username management with availability checks, and numerous bug fixes across plugins, OAuth providers, and core authentication features.