feat(web): cache dashboard aggregations with version invalidation

reaction_board/cli.py

@@ -433,6 +433,8 @@ def cmd_run(args, logger: JsonLogger, *, serve_web: bool = False) -> int:
                 ttl_days=cfg.schedule.candidate_ttl_days
             )
             expired = repo.expire_fav_actions()
+            if removed or expired:
+                repo.bump_cache_version("videos")
             logger.info(
                 "cleanup.done",
                 candidates_removed=removed, fav_actions_expired=expired,