Add web push notification system for user engagement and updates

Implement a web push notification system, including service worker integration, user subscription management, and an admin interface for sending broadcast messages.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 23852c00-4779-460a-9e0c-d09fee4b6c92
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: f585829f-898b-492f-82a5-11f4a76c87fb
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/f209e72a-0939-48fa-84fc-57854de71967/23852c00-4779-460a-9e0c-d09fee4b6c92/ICRgny1
Replit-Helium-Checkpoint-Created: true

client/public/sw.js

@@ -0,0 +1,31 @@
+self.addEventListener("push", (event) => {
+  let data = { title: "FOLX TV", body: "Neuer Inhalt verfügbar!", url: "/" };
+  try {
+    data = event.data.json();
+  } catch (e) {}
+  event.waitUntil(
+    self.registration.showNotification(data.title, {
+      body: data.body,
+      icon: "/favicon.png",
+      badge: "/favicon.png",
+      data: { url: data.url || "/" },
+    })
+  );
+});
+
+self.addEventListener("notificationclick", (event) => {
+  event.notification.close();
+  let url = event.notification.data?.url || "/";
+  if (!url.startsWith("/") || url.startsWith("//")) url = "/";
+  event.waitUntil(
+    clients.matchAll({ type: "window", includeUncontrolled: true }).then((clientList) => {
+      for (const client of clientList) {
+        if (client.url.includes(self.location.origin) && "focus" in client) {
+          client.navigate(url);
+          return client.focus();
+        }
+      }
+      return clients.openWindow(url);
+    })
+  );
+});