fix(deps): update dependency better-auth to v1.4.0-beta.21 (#28)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package.json

@@ -16,7 +16,7 @@
     "oidc": "node dev-auth/oidc-provider.mjs"
   },
   "dependencies": {
-    "better-auth": "1.4.0-beta.20",
+    "better-auth": "1.4.0-beta.21",
     "next": "16.0.3",
     "react": "19.2.0",
     "react-dom": "19.2.0"