refactor(plex): convert browse.py + rollup db.query() to 2.0 select() (wave 2)

Completes the plex-package 1.x->2.0 conversion, behaviour-equivalent (full
suite 253 passed, 2 skipped; the characterization net locks every path):
- routes/plex/browse.py (61 sites): libraries, facets (the wsq builder +
  jsonb genre unnest), collections, playlists (+ bulk add/remove/reorder),
  seasons, people/cards, collection strips, episode-nav, item detail, and
  the unified_library union builder.
- plex/rollup.py: agg_subquery now returns a select(); state_map executes it
  (the atomic unit coupled to unified_library via .subquery()).

Query builders -> select(); .filter/.filter_by -> .where; terminals ->
db.execute(...).scalars()/.all()/db.scalar(...); bulk .delete()/.update() ->
execute(delete()/update()). Zero db.query()/.filter_by remain in the package.

backend/app/plex/rollup.py

@@ -3,7 +3,7 @@
 Drives the show/season grid badges and the Resume / Play-from-start / mark-all buttons.
 """
 
-from sqlalchemy import and_, case, func, or_
+from sqlalchemy import and_, case, func, or_, select
 from sqlalchemy.orm import Session, aliased
 
 from app.models import PlexItem, PlexState
@@ -47,7 +47,7 @@ def agg_subquery(db: Session, user_id: int):
     grid by aggregate watch-state and (b) compute each card's badge."""
     ps = aliased(PlexState)
     return (
-        db.query(
+        select(
             PlexItem.show_id.label("show_id"),
             func.count(PlexItem.id).label("total"),
             func.count(case((ps.status == "watched", 1))).label("watched"),
@@ -64,7 +64,7 @@ def agg_subquery(db: Session, user_id: int):
             ).label("inprog"),
         )
         .outerjoin(ps, and_(ps.item_id == PlexItem.id, ps.user_id == user_id))
-        .filter(PlexItem.kind == "episode", PlexItem.show_id.isnot(None))
+        .where(PlexItem.kind == "episode", PlexItem.show_id.isnot(None))
         .group_by(PlexItem.show_id)
     )
 
@@ -72,5 +72,7 @@ def agg_subquery(db: Session, user_id: int):
 def state_map(db: Session, user_id: int, show_ids: list[int]) -> dict[int, str]:
     if not show_ids:
         return {}
-    rows = agg_subquery(db, user_id).filter(PlexItem.show_id.in_(show_ids)).all()
+    rows = db.execute(
+        agg_subquery(db, user_id).where(PlexItem.show_id.in_(show_ids))
+    ).all()
     return {r.show_id: show_status(r.total, r.watched, r.inprog) for r in rows}