Notify super admins on new user registration (bell + email)

When a new user registers, all super_admin users receive:
- A database notification shown in the bell (type: new_user), with the
  new user's avatar and a link to their channel
- An email congratulating them with the new member's name, email,
  join date, gender, and nationality, plus a View Profile CTA

Notification rendering in app.blade.php refactored into notifHref() and
notifThumb() helpers so new_user notifications link to /channel/{slug}
and show a circular avatar instead of a video thumbnail. Also fixed the
legacy /storage/thumbnails/ path to /media/thumbnails/ for video notifications.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

app/Notifications/NewUserRegistered.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace App\Notifications;
+
+use App\Models\User;
+use Illuminate\Notifications\Notification;
+use Illuminate\Notifications\Messages\MailMessage;
+
+class NewUserRegistered extends Notification
+{
+    public function __construct(public User $newUser) {}
+
+    public function via(object $notifiable): array
+    {
+        return ['database', 'mail'];
+    }
+
+    public function toArray(object $notifiable): array
+    {
+        return [
+            'type'         => 'new_user',
+            'user_id'      => $this->newUser->id,
+            'user_name'    => $this->newUser->name,
+            'user_email'   => $this->newUser->email,
+            'user_avatar'  => $this->newUser->avatar_url,
+            'user_channel' => $this->newUser->channel,
+        ];
+    }
+
+    public function toMail(object $notifiable): MailMessage
+    {
+        return (new MailMessage)
+            ->subject('New member joined TAKEONE 🎉')
+            ->view('emails.new-user-registered', [
+                'newUser' => $this->newUser,
+                'admin'   => $notifiable,
+            ]);
+    }
+}