fix: protect server counter callers and fix tariff change detection

- Wrap unprotected add/remove_user_to/from_servers calls in try/except
  in miniapp.py and cabinet subscription.py to prevent 500 errors
- Fix is_tariff_change to include classic-to-tariff transitions
  (subscription.tariff_id=None → new tariff_id) so purchased traffic
  is properly reset when switching modes

app/cabinet/routes/subscription.py

@@ -3216,7 +3216,10 @@ async def update_countries(
         added_server_ids = await get_server_ids_by_uuids(db, added)
         if added_server_ids:
             await add_subscription_servers(db, user.subscription, added_server_ids, added_server_prices)
-            await add_user_to_servers(db, added_server_ids)
+            try:
+                await add_user_to_servers(db, added_server_ids)
+            except Exception as e:
+                logger.error(f'Ошибка обновления счётчика серверов: {e}')
 
     # Update connected squads
     user.subscription.connected_squads = selected_countries

app/database/crud/subscription.py

@@ -357,8 +357,9 @@ async def extend_subscription(
     )
 
     # Определяем, происходит ли СМЕНА тарифа (а не продление того же)
+    # Включает переход из классического режима (tariff_id=None) в тарифный
     is_tariff_change = (
-        tariff_id is not None and subscription.tariff_id is not None and tariff_id != subscription.tariff_id
+        tariff_id is not None and (subscription.tariff_id is None or tariff_id != subscription.tariff_id)
     )
 
     if is_tariff_change:

app/webapi/routes/miniapp.py

@@ -5926,7 +5926,10 @@ async def update_subscription_servers_endpoint(
 
     if added_server_ids:
         await add_subscription_servers(db, subscription, added_server_ids, added_server_prices)
-        await add_user_to_servers(db, added_server_ids)
+        try:
+            await add_user_to_servers(db, added_server_ids)
+        except Exception as e:
+            logger.error(f'Ошибка обновления счётчика серверов (add): {e}')
 
     removed_server_ids = [
         catalog[uuid].get('server_id') for uuid in removed if catalog[uuid].get('server_id') is not None
@@ -5934,7 +5937,10 @@ async def update_subscription_servers_endpoint(
 
     if removed_server_ids:
         await remove_subscription_servers(db, subscription.id, removed_server_ids)
-        await remove_user_from_servers(db, removed_server_ids)
+        try:
+            await remove_user_from_servers(db, removed_server_ids)
+        except Exception as e:
+            logger.error(f'Ошибка обновления счётчика серверов (remove): {e}')
 
     ordered_selection = []
     seen_selection = set()