Implement buy flow and migrate DTOs to schemas

Move DTO definitions from dto/ to schemas/ and update imports.
Add buy handler with FSM state management for device selection,
whitelist toggling, and duration choice. Include pricing logic,
inline keyboards, and new configuration fields.

handlers/support.py

@@ -6,7 +6,7 @@ from aiogram.types import CallbackQuery, Message
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from config import settings
-from dto.di import DependenciesDTO
+from schemas.di import DependenciesDTO
 from services.user_service import UserServiceException
 from states.support import SupportStorage
 from texts import GENERAL_PROCESSING, STANDARD_FALLBACK, SUPPORT_INIT, SUPPORT_MSG_SENT