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/app/plex/query.py

@@ -236,7 +236,7 @@ def apply_meta_filters(q, model, p: dict, lang: str = "en"):
 # The 4 classes the feed filter + facet expose, derived from the stored `playable` + `transcode_hw`.
 # ONE definition (this SQL CASE) so the filter WHERE and the facet counts can't drift: `playable_conds`
 # filters on it, `facets` groups by it. transcode_hw IS NOT True groups NULL (unprobed) with software.
-# Public — it is the shared source of truth imported by routes.plex.browse (facet order + zero-fill).
+# Public — it is the shared source of truth imported by plex.library (facet order + zero-fill).
 PLAYBACK_CLASSES = ("direct", "remux", "transcode_hw", "transcode_sw")