Layer-3 backstop: re-index content that SHOULD be searchable but is missing from media_search_index_v1.

The search index is written at three points — end of analysis (media_metadata_service:upsert at analysis completion), mint completion (ownership_recovery_worker after ownership flips active), and here. This sweep exists because the first two are event-triggered and can be missed: analysis running before a mint completes leaves the piece un-indexed until something re-runs upsert. This makes listing self-healing, not dependent on a single trigger.

Selects contents_v2 rows that are media_analysed==True AND minted (ownership_contract_address set AND ownership_status=='active') AND published (discoverable OR has an external URL) BUT absent from the index, and upserts them. upsert_search_index self-gates on minted + metadata presence, so a row that no longer qualifies is skipped (and any stale index doc deleted) inside the upsert — this sweep only decides what to check.

Called by Cloud Scheduler (needs a new job — see TODO). Best-effort, batched.