fix: send notification of student joining course to all teachers

apps/dashboard/src/routes/invite/s/[hash]/+page.svelte

@@ -95,13 +95,17 @@
         courseName: data.name
       });
 
-      // Send notification to teacher(s) that a student has joined the course.
+      // Send notification to all teacher(s) that a student has joined the course.
+      Promise.all(
+        teachers.map((email) =>
           triggerSendEmail(NOTIFICATION_NAME.TEACHER_STUDENT_JOINED, {
-        to: teachers[0],
+            to: email,
             courseName: data.name,
             studentName: $profile.fullname,
             studentEmail: $profile.email
-      });
+          })
+        )
+      );
 
       // go to lms
       return goto('/lms');