Delegate invite persistence to InviteRepository

- Add create(), update(), and reload_with_relationships() methods to InviteRepository
- Update InviteService to use repository methods instead of direct db operations

backend/services/invite.py

@@ -147,20 +147,10 @@ class InviteService:
                 godfather_id=godfather_id,
                 status=InviteStatus.READY,
             )
-            self.db.add(invite)
             try:
-                await self.db.commit()
-                await self.db.refresh(invite)
+                invite = await self.invite_repo.create(invite)
                 # Reload with relationships
-                from sqlalchemy import select
-                from sqlalchemy.orm import joinedload
-
-                result = await self.db.execute(
-                    select(Invite)
-                    .options(joinedload(Invite.godfather), joinedload(Invite.used_by))
-                    .where(Invite.id == invite.id)
-                )
-                invite = result.scalar_one()
+                invite = await self.invite_repo.reload_with_relationships(invite.id)
                 break
             except IntegrityError:
                 await self.db.rollback()
@@ -200,7 +190,4 @@ class InviteService:
 
         invite.status = InviteStatus.REVOKED
         invite.revoked_at = datetime.now(UTC)
-        await self.db.commit()
-        await self.db.refresh(invite)
-
-        return invite
+        return await self.invite_repo.update(invite)