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)/admin/school/grades/insights/page.tsx

@@ -3,6 +3,8 @@ import type { Metadata } from "next"
 import type { JSX } from "react"
 import { BarChart3 } from "lucide-react"
 
+import { requirePermission } from "@/shared/lib/auth-guard"
+import { Permissions } from "@/shared/types/permissions"
 import { getGrades } from "@/modules/school/data-access"
 import { getGradeHomeworkInsights } from "@/modules/classes/data-access"
 import { EmptyState } from "@/shared/components/ui/empty-state"
@@ -25,6 +27,7 @@ export default async function AdminGradeInsightsPage({
 }: {
   searchParams: Promise<SearchParams>
 }): Promise<JSX.Element> {
+  await requirePermission(Permissions.SCHOOL_MANAGE)
   const params = await searchParams
   const gradeId = getSearchParam(params, "gradeId")
   const selected = gradeId && gradeId !== "all" ? gradeId : ""