fix architecture and write new tests

apps/admin/src/app/dashboard/billing/page.tsx

@@ -467,14 +467,13 @@ export default function AdminBillingPage() {
   )
 
   async function api<T>(path: string, init?: RequestInit): Promise<T> {
-    const token = localStorage.getItem('admin_token')
     const res = await fetch(`${ADMIN_API_BASE}${path}`, {
       ...init,
       headers: {
         'Content-Type': 'application/json',
-        ...(token ? { Authorization: `Bearer ${token}` } : {}),
         ...(init?.headers ?? {}),
       },
+      credentials: 'include',
       cache: 'no-store',
     })
     if (res.headers.get('content-type')?.includes('application/pdf')) {