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)/teacher/lesson-plans/new/page.tsx

@@ -1,8 +1,10 @@
 import type { JSX } from "react"
+import { Suspense } from "react"
 import Link from "next/link"
 import { ArrowLeft } from "lucide-react"
 import { getTranslations } from "next-intl/server"
 import { Button } from "@/shared/components/ui/button"
+import { Skeleton } from "@/shared/components/ui/skeleton"
 import { TemplatePicker } from "@/modules/lesson-preparation/components/template-picker"
 
 export const dynamic = "force-dynamic"
@@ -20,7 +22,20 @@ export default async function NewLessonPlanPage(): Promise<JSX.Element> {
         </Button>
         <h1 className="text-2xl font-bold tracking-tight">{t("title.new")}</h1>
       </div>
-      <TemplatePicker />
+      <Suspense
+        fallback={
+          <div className="max-w-3xl mx-auto p-6 space-y-6">
+            <Skeleton className="h-10 w-full" />
+            <div className="grid grid-cols-1 md:grid-cols-2 gap-3">
+              {Array.from({ length: 4 }).map((_, i) => (
+                <Skeleton key={i} className="h-[100px] w-full" />
+              ))}
+            </div>
+          </div>
+        }
+      >
+        <TemplatePicker />
+      </Suspense>
     </div>
   )
 }