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)/messages/compose/loading.tsx

@@ -0,0 +1,40 @@
+import { Card, CardContent, CardHeader } from "@/shared/components/ui/card"
+import { Skeleton } from "@/shared/components/ui/skeleton"
+
+export default function ComposeLoading() {
+  return (
+    <div className="flex h-full flex-col p-8">
+      <div className="mx-auto w-full max-w-3xl space-y-6">
+        <div className="space-y-2">
+          <Skeleton className="h-8 w-48" />
+          <Skeleton className="h-4 w-64" />
+        </div>
+
+        <Card>
+          <CardHeader>
+            <Skeleton className="h-5 w-32" />
+          </CardHeader>
+          <CardContent className="space-y-4">
+            <div className="space-y-2">
+              <Skeleton className="h-4 w-16" />
+              <Skeleton className="h-10 w-full" />
+            </div>
+            <div className="space-y-2">
+              <Skeleton className="h-4 w-20" />
+              <Skeleton className="h-10 w-full" />
+            </div>
+            <div className="space-y-2">
+              <Skeleton className="h-4 w-16" />
+              <Skeleton className="h-32 w-full" />
+            </div>
+          </CardContent>
+        </Card>
+
+        <div className="flex justify-end gap-3">
+          <Skeleton className="h-10 w-24" />
+          <Skeleton className="h-10 w-28" />
+        </div>
+      </div>
+    </div>
+  )
+}