Refactor bot handlers and keyboards; implement admin features

- Removed unused prehandling, referrals, support, and states files.
- Updated admin and client handlers to improve structure and functionality.
- Introduced admin filters and routers for better access control.
- Added new billing and deposit functionalities for client interactions.
- Enhanced keyboard layouts for admin and client menus.
- Implemented promotion handling for admin users.
- Updated configuration to include admin settings.
- Improved utility functions for quote fetching and menu text building.
- Added common handlers for undefined commands and message deletions.

bot/handlers/system/__init__.py

@@ -0,0 +1,4 @@
+from .common import router as common_router
+from .prehandling import router as prehandling_router
+
+routers = [common_router, prehandling_router]

bot/handlers/system/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()

bot/handlers/system/prehandling.py

@@ -0,0 +1,9 @@
+from aiogram import F, Router
+from aiogram.types import Message
+
+router = Router()
+
+
+@router.message(F.chat.type != "private")
+async def prehandle_non_private(msg: Message):
+    return