feat(plex): the people are local — bios and portraits fetched ahead, not on the click (E30 S6)

A person's TMDB bio was fetched only when their page was first opened, off the request path, so the first
open showed no bio and the page never asked again (2 of 18,202 linked people were ever enriched).

- people_enrich scheduler job (every 10 min, 300 per run): linked people's bios from TMDB and their
  portraits into the image cache, the most-credited people first. A failed TMDB lookup ends the batch.
- Portraits are resized through Plex's photo transcoder to a 320 box (~15 KB instead of ~170 KB; the
  person-image proxy uses the same cache key, and a full-size original is removed as its small twin lands).
- The person response says `enriching` while a bio is on its way (a person the job hasn't reached yet).
- "Known for" is ranked by vote count, without guest visits as themselves (talk shows had crowded out the
  films: Tom Cruise had 14 of 15), with directed works, from a 40-deep pool; the page shows up to 15.
  Migration 0093 un-stamps enriched people so the job refetches them.
- A phased job result (backfill, people_enrich) now counts as a change for the audit trail; before, an
  automatic backfill run that added videos was never audited.
- HU: the watch reconcile job reads "egyeztetés" (a leftover from the S5 sweep).

backend/tests/test_plex_person.py

@@ -133,6 +133,7 @@ def test_person_detail_unknown_name_is_empty(db, monkeypatch, override_dep):
         "place_of_birth": None,
         "known_for_department": None,
         "also_known_as": [],
+        "enriching": False,
         "known_for": [],
         "movies": [],
         "shows": [],