fix: patch P0 security vulnerabilities and critical UX issues across 6 modules

Security: Add admin/layout.tsx auth guard; Add requirePermission() to 12 admin pages

Dashboard: Fix StudentStatsGrid rendering; Fix teacher greeting; Add loading/error boundaries; Fix col-span; Add metadata

Announcements: Fix audience filtering; Add user detail page; Trigger notifications on publish; Pass classes data; Add loading.tsx

Messages: Implement soft delete; Add unread badge with polling; Add notification dropdown polling; Add keyword search; Add quiet hours DND

Management: Add loading/error for 9 admin routes; Fix admin-classes-view to use Select for school/grade

Profile/Settings: Add loading/error; Fix parent role routing; Create ParentSettingsView; Integrate AiProviderSettingsCard; Add Tab URL persistence; Add logout confirm; Add avatar; Fix Progress arbitrary class

Schema: Add senderDeletedAt/receiverDeletedAt to messages; Add quietHours to notificationPreferences; Add uniqueIndex import

Docs: Update architecture docs 004/005

src/app/(dashboard)/announcements/[id]/page.tsx

@@ -0,0 +1,36 @@
+import { notFound } from "next/navigation"
+import type { Metadata } from "next"
+import type { JSX } from "react"
+
+import { requirePermission } from "@/shared/lib/auth-guard"
+import { Permissions } from "@/shared/types/permissions"
+import { getAnnouncementById } from "@/modules/announcements/data-access"
+import { AnnouncementDetail } from "@/modules/announcements/components/announcement-detail"
+
+export const metadata: Metadata = {
+  title: "Announcement - Next_Edu",
+}
+
+export const dynamic = "force-dynamic"
+
+export default async function AnnouncementDetailPage({
+  params,
+}: {
+  params: Promise<{ id: string }>
+}): Promise<JSX.Element> {
+  const { id } = await params
+  await requirePermission(Permissions.ANNOUNCEMENT_READ)
+
+  const announcement = await getAnnouncementById(id)
+  if (!announcement) notFound()
+
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <AnnouncementDetail
+        announcement={announcement}
+        canManage={false}
+        backHref="/announcements"
+      />
+    </div>
+  )
+}