Add full notification preferences system

Users can now control which in-app and email notifications they receive
from their Settings tab on their channel page.

Bell (in-app) preferences:
- New comment on my video (default: on)
- Reply to my comment (default: on)
- Comment liked (default: on)
- Video liked (default: on)
- New subscriber (default: on)
- New video from channels I follow (default: on)
- New post from channels I follow (default: on)
- New user registration — super admins only (default: on)

Email preferences (same set plus):
- Comment liked (default: off — too noisy)
- Video liked (default: off — too noisy)
- New post from channels I follow (default: off)
- My video finished processing (default: on)
- Weekly activity digest every Monday (default: on)
- New user registration — super admins only (default: on)

Implementation:
- Migration: notification_preferences JSON column on users table
- User::notificationPref($key) helper with typed defaults
- All existing notification classes updated to check prefs in via()
- 4 new notification classes: NewSubscriberNotification,
  VideoLikedNotification, NewPostNotification, WeeklyDigestNotification
- 8 new email views matching existing dark theme
- SendWeeklyDigest artisan command, scheduled every Monday 09:00
- NewSubscriberNotification wired into UserController::toggleSubscribe
- VideoLikedNotification wired into UserController::toggleLike
- NewPostNotification wired into PostController::store (to all subscribers)
- Bell renderer updated for new_subscriber, video_like, new_post types
- Preferences saved via AJAX (POST /settings/notifications) — instant
  toggle with automatic revert on failure

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

app/Notifications/NewCommentNotification.php

@@ -5,6 +5,7 @@ namespace App\Notifications;
 use App\Models\Comment;
 use App\Models\User;
 use App\Models\Video;
+use Illuminate\Notifications\Messages\MailMessage;
 use Illuminate\Notifications\Notification;
 use Illuminate\Support\Str;
 
@@ -18,7 +19,10 @@ class NewCommentNotification extends Notification
 
     public function via(object $notifiable): array
     {
-        return ['database'];
+        $ch = [];
+        if ($notifiable->notificationPref('notif_new_comment'))  $ch[] = 'database';
+        if ($notifiable->notificationPref('email_new_comment'))  $ch[] = 'mail';
+        return $ch;
     }
 
     public function toArray(object $notifiable): array
@@ -35,4 +39,16 @@ class NewCommentNotification extends Notification
             'comment_preview'  => Str::limit($this->comment->body, 80),
         ];
     }
+
+    public function toMail(object $notifiable): MailMessage
+    {
+        return (new MailMessage)
+            ->subject($this->commenter->name . ' commented on your video')
+            ->view('emails.new-comment', [
+                'video'    => $this->video,
+                'comment'  => $this->comment,
+                'commenter'=> $this->commenter,
+                'recipient'=> $notifiable,
+            ]);
+    }
 }