The content-warning include/exclude filter (and its count) ran a correlated
page_content_warnings->pages->chapters join per candidate manga — O(mangas *
pages) on every filtered list. Add a manga_content_warnings(manga_id, warning)
table holding each manga's deduped warning union, maintained by triggers that
recompute an affected manga's set (delete+reinsert of the tiny five-label set,
robust across page/chapter/manga cascade deletes), backfilled in the migration.
The filter is now a single indexed lookup.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
