add gamification characters (Duolingo-style mascot catalog)

New progress.Character model: an admin-managed catalog (same pattern as
subscription.Plan) of selectable mascots, each unlocked once the user's
XP crosses unlock_xp. No separate ownership table yet — unlocking is a
pure function of UserStats.xp, kept intentionally minimal since this is
the first of an incremental rollout the senior asked for.

- GET /api/characters — catalog with per-user unlocked/selected flags
- POST /api/characters/select — picks an active character, rejecting
  ones the user hasn't unlocked yet
- UserStats.selected_character_id tracks the pick
- seed_test_data now seeds 4 sample characters (owl/fox/turtle/lion)
  for local/staging testing

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

accounts/management/commands/seed_test_data.py

@@ -134,6 +134,9 @@ class Command(BaseCommand):
             BugReport.objects.filter(user_id__in=user_ids).delete()
             FamilyLink.objects.filter(parent_user_id__in=user_ids).delete()
 
+        from progress.models import Character
+        Character.objects.filter(slug__startswith='seed-').delete()
+
         Plan.objects.filter(title__startswith=SEED_TAG).delete()
         DiscountCode.objects.filter(code='SEEDTEST10').delete()
         Offer.objects.filter(code='SEEDTRIAL7').delete()
@@ -153,6 +156,7 @@ class Command(BaseCommand):
     def _seed(self):
         main_user, guest_user, parent_user, child_user, referred_user = self._seed_accounts()
         self._seed_content_and_progress(main_user)
+        self._seed_characters()
         self._seed_ai_tutor(main_user)
         plan_monthly, plan_yearly = self._seed_subscription_and_payment(main_user)
         self._seed_discount(main_user)
@@ -303,6 +307,26 @@ class Command(BaseCommand):
             'content/progress: 1 پایه، 1 مبحث، 2 Node، 2 درس، 2 سوال و پیشرفتِ کاربرِ اصلی آماده شد.'
         ))
 
+    # -- گیمیفیکیشن: کاراکترها -------------------------------------------------
+    def _seed_characters(self):
+        from progress.models import Character
+
+        # unlock_xp پلکانی، هماهنگ با xp=10ی کاربرِ اصلی که بالاتر ساخته شد:
+        # فقط اولین کاراکتر (unlock_xp=0) براش باز است، بقیه هنوز قفلن —
+        # برای این‌که هم مسیرِ «باز» و هم مسیرِ «قفل» در تست دستی قابل‌دیدن باشه.
+        characters = [
+            ('seed-owl', f'{SEED_TAG} جغد کنجکاو', 'owl', 0, 1),
+            ('seed-fox', f'{SEED_TAG} روباه باهوش', 'fox', 100, 2),
+            ('seed-turtle', f'{SEED_TAG} لاک‌پشت صبور', 'turtle', 300, 3),
+            ('seed-lion', f'{SEED_TAG} شیر شجاع', 'lion', 600, 4),
+        ]
+        for slug, name, icon, unlock_xp, order in characters:
+            Character.objects.get_or_create(
+                slug=slug, defaults=dict(name=name, icon=icon, unlock_xp=unlock_xp, order=order),
+            )
+
+        self.stdout.write(self.style.SUCCESS(f'progress: {len(characters)} کاراکترِ گیمیفیکیشن آماده شد.'))
+
     # -- ai_tutor -------------------------------------------------------------
     def _seed_ai_tutor(self, main_user):
         from ai_tutor.models import Conversation, Message, MessageFeedback