refactor: use betterauth instead of workos

packages/convex/convex.config.ts

@@ -0,0 +1,7 @@
+import betterAuth from "@convex-dev/better-auth/convex.config"
+import { defineApp } from "convex/server"
+
+const app = defineApp()
+app.use(betterAuth)
+
+export default app