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/accounts/index.tsx

@@ -0,0 +1,14 @@
+import { createFileRoute } from '@tanstack/react-router'
+
+export const Route = createFileRoute('/_authenticated/accounts/')({
+  component: AccountsListPage,
+})
+
+function AccountsListPage() {
+  return (
+    <div>
+      <h1 className="text-2xl font-bold">Accounts</h1>
+      <p className="text-muted-foreground mt-2">Account list — coming next phase</p>
+    </div>
+  )
+}

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' })
+  },
+})