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

services/user_service.py

@@ -1,3 +1,5 @@
+import logging
+
 from aiogram import Bot
 from aiogram.types import Message, ReactionTypeEmoji, User as TelegramUser
 from remnawave import RemnawaveSDK
@@ -21,6 +23,8 @@ from texts import (
     TICKET_STATUS_EMOJIS,
 )
 
+logger = logging.getLogger(__name__)
+
 
 class UserServiceError(Exception): ...
 
@@ -261,3 +265,16 @@ class UserService:
         ticket = await self.ticket_repository.get_ticket_by_thread_id(session, thread_id=thread_id)
 
         return await self.user_repository.get_referal_by_user_id(session, ticket.creator_id)
+
+    async def send_promotion_to_users(self, session: AsyncSession, msg: Message) -> list[User]:
+        users = await self.user_repository.get_users(session)
+
+        sent: list[User] = []
+        for user in users:
+            try:
+                await msg.copy_to(user.id)
+                sent.append(user)
+            except Exception:
+                logger.critical("failed to send a message to user %d.", user.id, exc_info=True)
+
+        return sent