feat: add admin login page and authentication logic with form handling

app/routes/_admin.lg-admin.tsx

@@ -1,6 +1,7 @@
-import { Outlet } from 'react-router'
+import { Outlet, redirect } from 'react-router'
 
 import { getStaff } from '~/apis/admin/get-staff'
+import { AUTH_PAGES } from '~/configs/pages'
 import { AdminProvider } from '~/contexts/admin'
 import { AdminDefaultLayout } from '~/layouts/admin/default'
 import { handleCookie } from '~/libs/cookies'
@@ -9,7 +10,14 @@ import type { Route } from './+types/_admin.lg-admin'
 
 export const loader = async ({ request }: Route.LoaderArgs) => {
   const { adminToken } = await handleCookie(request)
+  const { pathname } = new URL(request.url)
+  const isAuthPage = AUTH_PAGES.includes(pathname)
   let adminData
+
+  if (!isAuthPage && !adminToken) {
+    throw redirect('/lg-admin/login')
+  }
+
   if (adminToken) {
     const { data } = await getStaff({
       accessToken: adminToken,