cascade status: report duplicate primary keys in the derived index #479

After rows are keyed on (app_id, project_id, id), nothing in the storage layer can enforce the key on LanceDB (it has no constraints). A cheap health check in everos cascade status — count rows per table whose (app_id, project_id, id) repeats — would surface a bypassed write path immediately instead of as missing search results.

O(N) scan per table; fine for the sizes an embedded root holds. Deferred from the primary-key fix; a one-off script covers the upgrade check until then.