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In tariff mode, period_prices already includes servers and traffic costs. But show_payment_methods() and get_subscription_cost() were using the classic additive formula, adding server and traffic prices on top of the tariff price. Example: 49₽ tariff + 150₽ server + 150₽ traffic = 349₽ shown, should be 49₽. Now both functions detect tariff mode and only add extra device costs beyond the tariff's device_limit. Classic mode formula unchanged.