fix(plex,audit): E30 review round 2 — only a missing file is a dead headshot, one spelling per portrait

- warm_portraits: only 404/410 mark a headshot dead (measured: Plex answers a dead CDN file 404);
  a refused token or a 5xx is Plex failing, ends the run after three in a row and marks nothing.
  'failed' counts every failure, not only the current streak.
- is_portrait_url: plain path segments only — no dot or empty segment an HTTP client folds onto
  one file; person_thumb_url uses the same predicate (27 852 stored headshots all pass).
- Tests: Plex refusing (401/403/429/5xx), failures between successes (portraits and bios), the kept
  original served from cache, the audit_clear / demo_reset / discovery_purge rows' counts as data,
  and the 0094 backfill on real rows.

backend/tests/test_plex_overlay.py

@@ -6,10 +6,14 @@ Uses the DB lane (`db` fixture) — skipped when no Postgres is reachable. Runs
 (migrations 0063/0064) so the JSONB + STORED generated columns are exercised.
 """
 
+from alembic import command
+from alembic.config import Config
 from sqlalchemy import func, select
+from sqlalchemy.orm import Session
 
 import app.plex.sync as syncmod
 from app import sysconfig
+from app.db import engine
 from app.models import PlexItem, PlexLibrary, PlexShow
 from app.plex.genres import hu_genre, hu_genres
 from app.plex.sync import _apply_item, _canonical_guid, _sync_overlay
@@ -378,3 +382,38 @@ def test_the_genre_map_is_idempotent_and_keeps_an_unknown_word():
     assert once == ["Dráma", "Akció"]
     assert hu_genres(once) == once
     assert hu_genres(None) is None and hu_genres([]) is None
+
+
+def test_0094_gives_every_row_without_a_hungarian_list_one(db):
+    cfg = Config("alembic.ini")
+    command.downgrade(cfg, "0093_plex_person_known_for_votes")
+    upgraded = False
+    try:
+        with Session(engine) as s:
+            lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+            s.add(lib)
+            s.flush()
+            rows = {
+                "bare": PlexItem(genres=["Action", "Biography"]),
+                "overlaid": PlexItem(
+                    genres=["Action"], genres_hu=["Kaland"]
+                ),  # its twin's own list
+                "genreless": PlexItem(genres=[]),
+            }
+            for key, row in rows.items():
+                row.rating_key, row.library_id, row.kind, row.title = key, lib.id, "movie", key
+            show = PlexShow(rating_key="s", library_id=lib.id, title="s", genres=["Comedy"])
+            s.add_all([*rows.values(), show])
+            s.commit()
+            ids = {k: r.id for k, r in rows.items()}
+            show_id = show.id
+        command.upgrade(cfg, "head")
+        upgraded = True
+        with Session(engine) as s:
+            got = {k: s.get(PlexItem, i).genres_hu for k, i in ids.items()}  # type: ignore[union-attr]
+            show_hu = s.get(PlexShow, show_id).genres_hu  # type: ignore[union-attr]
+        assert got == {"bare": ["Akció", "Életrajzi"], "overlaid": ["Kaland"], "genreless": None}
+        assert show_hu == ["Vígjáték"]
+    finally:
+        if not upgraded:
+            command.upgrade(cfg, "head")