refactor: migrate betterauth to local install

also added a login page

Co-authored-by: Ona <no-reply@ona.com>

packages/convex/betterauth/convex.config.ts

@@ -0,0 +1,5 @@
+import { defineComponent } from "convex/server";
+
+const component = defineComponent("betterAuth");
+
+export default component;