feat(web): cache dashboard aggregations with version invalidation

reaction_board/services/folder_sync.py

@@ -200,6 +200,8 @@ class FolderSyncService:
             errors=len(summary.errors),
             elapsed=max(0, summary.finished_at - summary.started_at),
         )
+        if summary.added or summary.removed or summary.refreshed:
+            self.repo.bump_cache_version("videos")
         return summary
 
     def _sync_folder(