feat(app): add error/loading boundaries and update dashboard routes

- Add error.tsx and loading.tsx boundaries for admin, parent, student, teacher routes

- Add dashboard-error-fallback and dashboard-loading-skeleton components

- Add student/learning page, parent/leave routes, teacher textbook components

- Update existing app routes across auth, dashboard, and API endpoints

- Update proxy middleware and next-auth type declarations

src/app/(dashboard)/admin/dashboard/loading.tsx

@@ -0,0 +1,5 @@
+import { DashboardLoadingSkeleton } from "@/modules/dashboard/components/dashboard-loading-skeleton"
+
+export default function AdminDashboardLoading() {
+  return <DashboardLoadingSkeleton />
+}