Fix campaign update by re-fetching after flush

The previous refresh() call only reloaded relationships, not scalar
attributes like updated_at. Re-fetching via get_by_id ensures all
attributes and relationships are properly loaded.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/repositories/campaign_repository.py

@@ -90,9 +90,8 @@ class CampaignRepository:
                 setattr(campaign, key, value)
 
         await self.session.flush()
-        # Refresh to reload expired attributes and relationships after flush
-        await self.session.refresh(campaign, ["agency", "proofs"])
-        return campaign
+        # Re-fetch to get fresh data with eager-loaded relationships
+        return await self.get_by_id(campaign_id)
 
     async def delete(self, campaign_id: uuid.UUID) -> bool:
         """Delete a campaign and all related proofs."""