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

entrypoints/startup.sh

@@ -6,6 +6,14 @@ echo
 ruff check --fix
 black .
 
+echo "[+] checking psql availability"
+if ! pg_isready -h localhost -p 5432 ; then
+    echo "psql is down." >&2
+    exit 1
+fi
+echo "[+] psql is available!"
+echo
+
 echo "[+] Running migrations..."
 echo
 alembic upgrade head