feat: add Zustand stores and custom hooks

frontend-mobile/hooks/useAuth.ts

@@ -0,0 +1,19 @@
+import { useEffect } from 'react';
+import { useAuthStore } from '../store/authStore';
+
+export function useAuth() {
+  const { user, isLoading, isAuthenticated, login, logout, checkAuth } = useAuthStore();
+
+  useEffect(() => {
+    checkAuth();
+  }, []);
+
+  return {
+    user,
+    isLoading,
+    isAuthenticated,
+    login,
+    logout,
+    isAdmin: user?.is_admin ?? false,
+  };
+}