Delete all quality='canary' rows from eq_training_corpus and eq_wishlist.

Canary rows are written during automated self-test runs (see CANARY_PREFIXES / CANARY_WISHLIST_PREFIX). The server back-fills them at startup, but rows that arrive during a running deployment are not cleaned up until the next restart. This endpoint lets an operator flush them on demand without a restart.

Returns { training_corpus_deleted, wishlist_deleted } counts. Requires X-Admin-Token header.