feat(auth): enforce login route with global middleware

frontend/app/middleware/auth.global.ts

@@ -0,0 +1,20 @@
+export default defineNuxtRouteMiddleware(async (to) => {
+  const isLoginRoute = to.path === "/login";
+
+  const fetcher = import.meta.server ? useRequestFetch() : $fetch;
+  let authenticated = false;
+  try {
+    await fetcher("/api/auth/session", { method: "GET" });
+    authenticated = true;
+  } catch {
+    authenticated = false;
+  }
+
+  if (!authenticated && !isLoginRoute) {
+    return navigateTo("/login");
+  }
+
+  if (authenticated && isLoginRoute) {
+    return navigateTo("/");
+  }
+});