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)/student/learning/courses/loading.tsx

@@ -3,7 +3,7 @@ import { Skeleton } from "@/shared/components/ui/skeleton"
 
 export default function Loading() {
   return (
-    <div className="flex h-full flex-col space-y-8 p-8">
+    <div className="space-y-8">
       <div className="space-y-2">
         <Skeleton className="h-8 w-40" />
         <Skeleton className="h-4 w-52" />