refactor: remove unused authentication files and dependencies; update package.json to streamline dependencies and improve project structure

packages/backend/convex/betterAuth/adapter.ts

@@ -1,13 +0,0 @@
-import { createApi } from "@convex-dev/better-auth";
-import schema from "./schema";
-import { createAuth } from "../auth";
-
-export const {
-  create,
-  findOne,
-  findMany,
-  updateOne,
-  updateMany,
-  deleteOne,
-  deleteMany,
-} = createApi(schema, createAuth);