feat: refactor announcements page and layout to support sidebar slide-out functionality

- Replaced the existing announcement card and empty state components with imports from the new announcements directory.
- Introduced state management for the announcements sidebar in the LayoutDataProvider.
- Updated navigation items to handle announcements sidebar toggling.
- Integrated AnnouncementsSidebar into the LayoutShell for both mobile and desktop views.
- Enhanced sidebar handling to improve user experience when navigating announcements.

surfsense_web/components/announcements/AnnouncementsEmptyState.tsx

@@ -0,0 +1,18 @@
+"use client";
+
+import { BellOff } from "lucide-react";
+
+export function AnnouncementsEmptyState() {
+	return (
+		<div className="flex flex-col items-center justify-center py-16 text-center">
+			<div className="flex h-16 w-16 items-center justify-center rounded-full bg-muted mb-4">
+				<BellOff className="h-7 w-7 text-muted-foreground" />
+			</div>
+			<h3 className="text-lg font-semibold">No announcements</h3>
+			<p className="mt-1 text-sm text-muted-foreground max-w-sm">
+				You're all caught up! New announcements will appear here.
+			</p>
+		</div>
+	);
+}
+