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/repositories/invite.py

@@ -80,3 +80,49 @@ class InviteRepository:
         query = query.order_by(desc(Invite.created_at)).offset(offset).limit(per_page)
         result = await self.db.execute(query)
         return list(result.scalars().all())
+
+    async def create(self, invite: Invite) -> Invite:
+        """
+        Create a new invite record.
+
+        Args:
+            invite: Invite instance to persist
+
+        Returns:
+            Created Invite record (committed and refreshed)
+        """
+        self.db.add(invite)
+        await self.db.commit()
+        await self.db.refresh(invite)
+        return invite
+
+    async def update(self, invite: Invite) -> Invite:
+        """
+        Update an existing invite record.
+
+        Args:
+            invite: Invite instance to update
+
+        Returns:
+            Updated Invite record (committed and refreshed)
+        """
+        await self.db.commit()
+        await self.db.refresh(invite)
+        return invite
+
+    async def reload_with_relationships(self, invite_id: int) -> Invite:
+        """
+        Reload an invite with all relationships eagerly loaded.
+
+        Args:
+            invite_id: ID of the invite to reload
+
+        Returns:
+            Invite record with relationships loaded
+        """
+        result = await self.db.execute(
+            select(Invite)
+            .options(joinedload(Invite.godfather), joinedload(Invite.used_by))
+            .where(Invite.id == invite_id)
+        )
+        return result.scalar_one()