fix logic and tests, update docker CI file

app/Services/Administrator/TeacherSubmissionNotificationService.php

@@ -2,6 +2,7 @@
 
 namespace App\Services\Administrator;
 
+use App\Mail\TeacherSubmissionReminderMail;
 use App\Models\ClassSection;
 use App\Models\TeacherSubmissionNotificationHistory;
 use App\Models\User;
@@ -88,9 +89,7 @@ class TeacherSubmissionNotificationService
 
             if (!empty($email) && filter_var($email, FILTER_VALIDATE_EMAIL)) {
                 try {
-                    Mail::html($body, function ($message) use ($email, $subject) {
-                        $message->to($email)->subject($subject);
-                    });
+                    Mail::to($email)->send(new TeacherSubmissionReminderMail($subject, $body));
                     $status = 'sent';
                 } catch (\Throwable $e) {
                     Log::error('Teacher submission notification failed: ' . $e->getMessage());
@@ -158,4 +157,4 @@ class TeacherSubmissionNotificationService
 
         return array_values($targets);
     }
-}
+}