refactor(plex): the browse, detail, people and collection pages read through queries and write through the service

The HTTP files browse, detail, people, collections and _shared do no database work of their own
now. New plex/queries.py (the rows a page shows, a user's watch state through userscope),
plex/service.py (the info pages' enrichment, a collection's editable flag, the row kept after a
failed follow-up read, the person bio's background fetch; none commits), plex/library.py (the
unified browse feed, its search and facets) and plex/collections.py (a collection's source,
editability, card, certificate and member order). Every watch-state join in the moved code names
its owner through owned_by.

Pins 354 -> 178 in 4 files; basedpyright baseline 132 -> 118.

backend/tests/test_plex_collection_sort.py

@@ -20,8 +20,8 @@ from app.main import app
 from app.models import User
 from app.plex.models import PlexCollection, PlexItem, PlexLibrary, PlexShow, PlexState
 from app.plex.query import PLEX_SORT_KEYS
-from app.routes.plex.browse import sort_column
-from app.routes.plex.collections import (
+from app.plex.library import sort_column
+from app.plex.collections import (
     DEFAULT_MEMBER_SORT,
     MEMBER_SORT_KEYS,
     Member,