feat: add admin promotion broadcast system and psql health check

- Add `/push` command for admins to broadcast messages to all users
  with approve/decline confirmation flow (handlers/ads.py)
- Add common handler for undefined commands and delete callback
- Add `UserRepository.get_users()` to fetch all users
- Add `UserService.send_promotion_to_users()` with error logging
- Add promotion confirmation keyboard and FSM state
- Add PostgreSQL availability check in startup.sh before migrations
- Add new text constants for promotion flow

handlers/common.py

@@ -0,0 +1,20 @@
+from aiogram import F, Router
+from aiogram.fsm.context import FSMContext
+from aiogram.types import CallbackQuery, Message
+
+from config import settings
+from texts import UNDEFINED_MESSAGE
+
+router = Router()
+
+
+@router.message(F.chat.id != settings.admin_group_id)
+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()