Add better-auth integration and update dependencies in package.json and bun.lock

packages/backend/convex/http.ts

@@ -0,0 +1,8 @@
+import { httpRouter } from "convex/server";
+import { authComponent, createAuth } from "./auth";
+
+const http = httpRouter();
+
+authComponent.registerRoutes(http, createAuth);
+
+export default http;