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

app/middleware/auth.global.ts

@@ -0,0 +1,6 @@
+export default defineNuxtRouteMiddleware((to, from) => {
+	const auth = useAuth()
+
+	if (!auth.refreshToken.value && !to.fullPath.includes("/auth"))
+		return navigateTo("/auth/signin")
+})