fix: изолировать stored_amount от downstream consumers в create_transaction

- stored_amount используется только для БД записи, оригинальный
  amount_kopeks передаётся в event emitter и contest service через abs()
- Добавлен func.abs() в leaderboard конкурсов (referral_contest.py)
- Предотвращает негативные суммы в событиях и рейтинге конкурсов

app/database/crud/referral_contest.py

@@ -197,7 +197,7 @@ async def get_contest_leaderboard(
         select(
             User,
             func.count(ReferralContestEvent.id).label('referral_count'),
-            func.coalesce(func.sum(ReferralContestEvent.amount_kopeks), 0).label('total_amount'),
+            func.coalesce(func.sum(func.abs(ReferralContestEvent.amount_kopeks)), 0).label('total_amount'),
         )
         .join(User, User.id == ReferralContestEvent.referrer_id)
         .where(

app/database/crud/transaction.py

@@ -40,13 +40,13 @@ async def create_transaction(
     created_at: datetime | None = None,
 ) -> Transaction:
     # SUBSCRIPTION_PAYMENT — always store as negative (debit from user balance)
-    if type == TransactionType.SUBSCRIPTION_PAYMENT and amount_kopeks > 0:
-        amount_kopeks = -amount_kopeks
+    # Keep original for downstream consumers (events, contests)
+    stored_amount = -amount_kopeks if type == TransactionType.SUBSCRIPTION_PAYMENT and amount_kopeks > 0 else amount_kopeks
 
     transaction = Transaction(
         user_id=user_id,
         type=type.value,
-        amount_kopeks=amount_kopeks,
+        amount_kopeks=stored_amount,
         description=description,
         payment_method=payment_method.value if payment_method else None,
         external_id=external_id,
@@ -62,7 +62,7 @@ async def create_transaction(
     logger.info(
         '💳 Создана транзакция: на ₽ для пользователя',
         type_value=type.value,
-        amount_kopeks=amount_kopeks / 100,
+        amount_kopeks=stored_amount / 100,
         user_id=user_id,
     )
 
@@ -76,8 +76,8 @@ async def create_transaction(
                 'transaction_id': transaction.id,
                 'user_id': user_id,
                 'type': type.value,
-                'amount_kopeks': amount_kopeks,
-                'amount_rubles': amount_kopeks / 100,
+                'amount_kopeks': abs(amount_kopeks),
+                'amount_rubles': abs(amount_kopeks) / 100,
                 'payment_method': payment_method.value if payment_method else None,
                 'external_id': external_id,
                 'is_completed': is_completed,
@@ -103,7 +103,7 @@ async def create_transaction(
             await referral_contest_service.on_subscription_payment(
                 db,
                 user_id,
-                amount_kopeks,
+                abs(amount_kopeks),
             )
         except Exception as exc:
             logger.debug('Не удалось записать событие конкурса для пользователя', user_id=user_id, exc=exc)