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/ads.py

@@ -0,0 +1,69 @@
+from aiogram import F, Router
+from aiogram.filters import Command
+from aiogram.fsm.context import FSMContext
+from aiogram.types import CallbackQuery, Message
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from config import settings
+from keyboards.admins import promotion_confirmation
+from keyboards.client import build_return_menu
+from schemas.di import DependenciesDTO
+from schemas.promotions import NewPromotionContext
+from states.admins import AdminStorage
+from texts import (
+    ADMIN_PROMOTION_CONFIRMATION,
+    ADMIN_PROMOTION_INIT,
+    ADMIN_STANDARD_FALLBACK,
+    SUCCESSFULLY_SENT_PROMOTION,
+)
+
+router = Router()
+
+
+@router.message(
+    F.chat.id == settings.admin_group_id, F.message_thread_id.is_(None), Command("push")
+)
+async def push_cmd(msg: Message, state: FSMContext):
+    await state.clear()
+
+    ctx = NewPromotionContext(creator_id=msg.from_user.id)
+    await msg.delete()
+    await msg.answer(ADMIN_PROMOTION_INIT, reply_markup=build_return_menu("delete", "❌"))
+
+    await state.set_state(AdminStorage.promotion_msg)
+    await state.set_data({"ctx": ctx})
+
+
+@router.message(F.chat.id == settings.admin_group_id, AdminStorage.promotion_msg)
+async def send_promotion(msg: Message, state: FSMContext):
+    data = await state.get_data()
+
+    ctx: NewPromotionContext | None = data.get("ctx")
+    if not ctx:
+        await msg.answer(ADMIN_STANDARD_FALLBACK)
+        return
+
+    ctx.message = msg
+    await msg.reply(ADMIN_PROMOTION_CONFIRMATION, reply_markup=promotion_confirmation)
+
+    await state.set_state(AdminStorage.promotion_msg)
+    await state.set_data({"ctx": ctx})
+
+
+@router.callback_query(AdminStorage.promotion_msg, F.data.in_(["approve", "decline"]))
+async def promotion_action(
+    cb: CallbackQuery, state: FSMContext, session: AsyncSession, deps: DependenciesDTO
+):
+    data = await state.get_data()
+    await state.clear()
+
+    await cb.message.delete()
+    if cb.data == "decline":
+        return
+    ctx: NewPromotionContext | None = data.get("ctx")
+    if not (ctx and ctx.creator_id and ctx.message):
+        await cb.message.answer(ADMIN_STANDARD_FALLBACK)
+        return
+
+    sent = await deps.user_service.send_promotion_to_users(session, ctx.message)
+    await cb.message.answer(SUCCESSFULLY_SENT_PROMOTION.format(user_count=len(sent)))