feat: add Teacher Admin role to four-tier permission system

Introduces a four-tier role system: Regular User → Student Admin →
Teacher Admin → Super Admin. Teacher Admin can manage own contests,
problemsets, and view classroom data. Student Admin (renamed from Admin)
retains problem management only.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

account/views/admin.py

@@ -105,7 +105,9 @@ class UserAdminAPI(APIView):
         user.admin_type = data["admin_type"]
         user.is_disabled = data["is_disabled"]
 
-        if data["admin_type"] == AdminType.ADMIN:
+        if data["admin_type"] == AdminType.STUDENT_ADMIN:
+            user.problem_permission = data["problem_permission"] or ProblemPermission.OWN
+        elif data["admin_type"] == AdminType.TEACHER_ADMIN:
             user.problem_permission = data["problem_permission"] or ProblemPermission.OWN
         elif data["admin_type"] == AdminType.SUPER_ADMIN:
             user.problem_permission = ProblemPermission.ALL

account/views/oj.py

@@ -432,7 +432,7 @@ class UserRankAPI(AsyncAPIView):
             n = 0
 
         profiles = UserProfile.objects.filter(
-            user__admin_type__in=[AdminType.REGULAR_USER, AdminType.ADMIN],
+            user__admin_type__in=[AdminType.REGULAR_USER, AdminType.STUDENT_ADMIN],
             user__is_disabled=False,
             user__username__icontains=username,
         ).select_related("user").filter(accepted_number__gte=0).order_by("-accepted_number", "submission_number")