Refactor: Move Navbar to MainLayout for consistency

Relocated the Navbar component to the MainLayout to streamline its rendering across dashboard pages. This eliminates redundant Navbar instances in individual pages, improving maintainability and reducing duplication.

frontend/src/app/(main)/dashboard/events/[slug]/page.tsx

@@ -42,7 +42,6 @@ export default function EventDetailPage() {
 
   return (
     <>
-      <Navbar />
       <div className="container">
         <h1>{event.title}</h1>
         <p>{event.description}</p>

frontend/src/app/(main)/dashboard/events/new/page.tsx

@@ -81,7 +81,6 @@ export default function CreateEventPage() {
 
   return (
     <>
-      <Navbar />
       <div className="container mx-auto px-4 py-12 max-w-4xl">
         <Card className="shadow-lg">
           <CardHeader>