fix: фиксы после рефакторинга

src/domain/external_channel.py

@@ -12,7 +12,7 @@ if TYPE_CHECKING:
 
 class ExternalChannel(TimestampedModel):
     id = fields.UUIDField(pk=True)
-    telegram_id = fields.BigIntField(unique=True, index=True)
+    telegram_id = fields.BigIntField(index=True)
     title = fields.CharField(max_length=255)
     username = fields.CharField(max_length=255, null=True, index=True)
     description = fields.TextField(null=True)
@@ -28,3 +28,4 @@ class ExternalChannel(TimestampedModel):
 
     class Meta:
         table = 'external_channel'
+        unique_together = (('user_id', 'telegram_id'),)