fix: autopay renewing trial subscriptions at classic-mode pricing

Three bugs caused trial subscriptions to be auto-renewed without a
tariff at arbitrary prices:

1. try_auto_extend_expired_after_topup: is_trial guard used truthiness
   check — NULL (legacy rows) passed as falsy. Changed to
   `is_trial is not False` (NULL-safe).

2. Multi-tariff branch: `not s.is_trial` treated NULL as not-trial.
   Changed to `s.is_trial is False`.

3. Telegram bot autopay toggle: no is_trial guard — users could enable
   autopay on trial subscriptions. Added trial check before enabling.

app/handlers/subscription/autopay.py

@@ -101,6 +101,18 @@ async def toggle_autopay(callback: types.CallbackQuery, db_user: User, db: Async
     enable = callback.data.startswith('autopay_enable')
 
     if enable:
+        # Trial subscriptions cannot use autopay
+        if subscription.is_trial or subscription.is_trial is None:
+            texts = get_texts(db_user.language)
+            await callback.answer(
+                texts.t(
+                    'AUTOPAY_NOT_AVAILABLE_TRIAL',
+                    'Автоплатеж недоступен для пробных подписок.',
+                ),
+                show_alert=True,
+            )
+            return
+
         # Classic subscriptions cannot use autopay when tariff mode is enabled
         if settings.is_tariffs_mode() and not subscription.tariff_id:
             texts = get_texts(db_user.language)

app/services/subscription_auto_purchase_service.py

@@ -2138,7 +2138,7 @@ async def try_auto_extend_expired_after_topup(
         from app.database.crud.subscription import get_all_subscriptions_by_user_id
 
         all_subs = await get_all_subscriptions_by_user_id(db, user.id)
-        expired_subs = [s for s in all_subs if s.status == SubscriptionStatus.EXPIRED.value and not s.is_trial]
+        expired_subs = [s for s in all_subs if s.status == SubscriptionStatus.EXPIRED.value and s.is_trial is False]
         if not expired_subs:
             subscription = None
         else:
@@ -2154,9 +2154,10 @@ async def try_auto_extend_expired_after_topup(
         return False
 
     # Only process expired subscriptions (not trial, not disabled)
+    # NULL-safe: is_trial can be None in legacy rows — treat as trial
     if subscription.status != SubscriptionStatus.EXPIRED.value:
         return False
-    if subscription.is_trial:
+    if subscription.is_trial is not False:
         return False
 
     # Only process subscriptions expired within the last 30 days