feat: add login page and auth guard

dashboard/src/lib/auth.ts

@@ -0,0 +1,35 @@
+export function getToken(): string | null {
+  if (typeof window === 'undefined') return null;
+  return localStorage.getItem('token');
+}
+
+export function setToken(token: string) {
+  localStorage.setItem('token', token);
+}
+
+export function removeToken() {
+  localStorage.removeItem('token');
+}
+
+export function isAuthenticated(): boolean {
+  return !!getToken();
+}
+
+export async function fetchWithAuth(url: string, options: RequestInit = {}) {
+  const token = getToken();
+  const headers = {
+    ...options.headers,
+    'Content-Type': 'application/json',
+    ...(token ? { Authorization: `Bearer ${token}` } : {}),
+  };
+
+  const res = await fetch(url, { ...options, headers });
+
+  if (res.status === 401) {
+    removeToken();
+    window.location.href = '/login';
+    throw new Error('Unauthorized');
+  }
+
+  return res;
+}