feat: creatives and external channels

src/domain/user.py

@@ -1,7 +1,16 @@
-from sqlalchemy.orm import Mapped
+from typing import TYPE_CHECKING
+
+from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from src import domain
 
+if TYPE_CHECKING:
+    from . import TargetChannel
+
 
 class User(domain.Base):
-    name: Mapped[str]
+    telegram_id: Mapped[int] = mapped_column(unique=True, index=True)
+    username: Mapped[str | None]
+
+    # Relationship with channels
+    target_channels: Mapped[list['TargetChannel']] = relationship(back_populates='user')