routes/plex/browse.py was a 1693-line god-module (libraries + facets +
collections + playlists + show/item detail + people). Split it into focused
sibling routers under the same /api/plex prefix — pure code motion, no SQL /
route-path / response-shape changes:
browse.py 1693 -> 469 (list_libraries, unified_library, facets)
collections.py (new 253) browse + admin collection editor; owns _collection_source
playlists.py (new 405) the user's orderable playlists
detail.py (new 438) show/item detail + enrichment; _lib_key lives here
people.py (new 139) cast/crew chips + person filmography
Cross-module helpers _norm_lang + _content_libs move to _shared.py (their one
home); detail imports _collection_source from collections (one-way, no cycle).
__init__.py includes the four new routers. Three DB-lane tests follow the moved
symbols (import path for _content_libs; monkeypatch targets for PlexClient /
_show_enrichment now on detail).
Behaviour-equivalent: ruff clean, 348 DB-lane pass (unchanged), parity net green.