feat: Implement payment notification system and API structure

- Added notifications for successful payments in `api/core/notifications.py`.
- Created main API entry point in `api/main.py` with FastAPI integration.
- Established routing structure in `api/routes/__init__.py` and `api/routes/pally.py` for handling payment callbacks.
- Developed billing handlers in `bot/handlers/billing.py` and `bot/handlers/buy.py` for subscription management.
- Introduced state management for user interactions in `bot/states/`.
- Created user interface elements in `bot/keyboards/` for navigation and payment processing.
- Set up middleware for dependency injection in `bot/middlewares/di.py`.
- Added support for user commands and interactions in `bot/handlers/common.py` and `bot/handlers/support.py`.
- Implemented logging and error handling throughout the bot's functionality.
- Created entry point script for API server in `entrypoints/api.sh`.

requirements.txt

@@ -7,4 +7,7 @@ pydantic-settings>=2.7.0
 python-dotenv
 aiohttp-socks
 alembic
-remnawave>=2.6.1
+remnawave>=2.6.1
+fastapi>=0.100.0
+uvicorn[standard]>=0.24.0
+python-multipart