Implement authentication composable with signin, signup, and session management; add route middleware for auth checks

app/utils/cfetch.ts

@@ -8,6 +8,8 @@ export const cfetch = async (
 ): Promise<AxiosResponse> => {
 	const baseUrl = import.meta.env.VITE_PUBLIC_BACKEND
 
+	if (!baseUrl) throw new Error("BACKEND URL not set")
+
 	const defaults: AxiosRequestConfig = {
 		baseURL: baseUrl,
 	}