Migration leaf split: main's 0054 hotfix migration vs dev's 0054–0059 #287

What: hotfix #283 added 0054_rebuild_long_text_search_indexes on main; dev already has 0054_add_source_identifier_metadata … 0059_event_search_cover_url.
Why it matters: the next dev→main release has two migration leaves and migrate fails until main is merged into dev with a merge migration.
Evidence: git ls-tree origin/dev api/migrations → 0053, 0054_add_source_identifier_metadata … 0059; main → 0053, 0054_rebuild_long_text_search_indexes.
Fix: not fixed — merge main into dev + makemigrations --merge (flagged on #283).