Update notification sound to notification.mp3

Replaces all references to hohoho.mp3 with notification.mp3 for notification sounds across the app. Moves AudioPreloader to layout component and removes duplicate usage. Adds a guard in BroadcastDialog to prevent duplicate sends.

components/layout/layout.tsx

@@ -5,6 +5,7 @@ import { useTheme } from "next-themes"
 import { usePathname } from "next/navigation"
 import Sidebar from "./sidebar"
 import UnifiedNotifications from "@/components/notifications/UnifiedNotifications"
+import { AudioPreloader } from "@/components/audio-preloader"
 import type React from "react"
 
 interface LayoutProps {
@@ -45,21 +46,24 @@ export default function Layout({ children }: LayoutProps) {
   }
 
   return (
-    <div className="flex h-screen">
-      <Sidebar />
-      <div className="w-full flex flex-1 flex-col">
-        {!isChatDetailPage && !isAdminPage && (
-          <header className="h-16 border-b border-border flex items-center justify-end px-6 bg-background">
-            <div className="flex items-center space-x-2">
-              <UnifiedNotifications />
-            </div>
-          </header>
-        )}
-        <main className={`flex-1 ${isChatDetailPage ? 'p-0 overflow-hidden' : 'p-6 overflow-auto'} bg-background relative`}>
-          {children}
-        </main>
+    <>
+      <AudioPreloader />
+      <div className="flex h-screen">
+        <Sidebar />
+        <div className="w-full flex flex-1 flex-col">
+          {!isChatDetailPage && !isAdminPage && (
+            <header className="h-16 border-b border-border flex items-center justify-end px-6 bg-background">
+              <div className="flex items-center space-x-2">
+                <UnifiedNotifications />
+              </div>
+            </header>
+          )}
+          <main className={`flex-1 ${isChatDetailPage ? 'p-0 overflow-hidden' : 'p-6 overflow-auto'} bg-background relative`}>
+            {children}
+          </main>
+        </div>
       </div>
-    </div>
+    </>
   )
 }