Scaffold @forte/admin package with React, Vite, shadcn/ui, TanStack Router

Sets up the admin frontend with login page, auth guard, API client, Zustand
auth store, and all shadcn/ui components. Vite proxies /v1 to backend in dev.

packages/admin/src/routes/_authenticated/index.tsx

@@ -0,0 +1,7 @@
+import { createFileRoute, redirect } from '@tanstack/react-router'
+
+export const Route = createFileRoute('/_authenticated/')({
+  beforeLoad: () => {
+    throw redirect({ to: '/accounts' })
+  },
+})