Locks the observable behaviour of the previously-untested Plex query hot
paths before the 2.0 conversion, so it can be proven behaviour-equivalent:
- unified_library: both/movie/show scope, added-desc ordering, the four
watch-state branches, search rank + episode grouping, pagination.
- rollup.state_map: new / in_progress / watched rollup.
- sync upsert idempotency: _sync_movies + _sync_shows run twice = no dup
rows, in-place update, episode->show linking.
Green on the current 1.x code (9 passed). The conversion commits must keep
these identical.