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`.

bot/handlers/common.py

@@ -0,0 +1,19 @@
+from aiogram import F, Router
+from aiogram.fsm.context import FSMContext
+from aiogram.types import CallbackQuery, Message
+
+from bot.texts import UNDEFINED_MESSAGE
+
+router = Router()
+
+
+@router.message()
+async def undefined_cmd(msg: Message):
+    await msg.delete()
+    await msg.answer(UNDEFINED_MESSAGE)
+
+
+@router.callback_query(F.data == "delete")
+async def delete_cb(cb: CallbackQuery, state: FSMContext):
+    await state.clear()
+    await cb.message.delete()