E5 S6: enriched person page (TMDB bio + birth facts + Known-for rail)

The person page now leads with a TMDB bio, lazily fetched the first time it's
opened (off the S2-linked `tmdb_person_id`) and then served from the row:

- Migration 0072: ADD-only nullable person columns on plex_people — biography,
  birthday, deathday, place_of_birth, known_for_department, also_known_as,
  known_for ([{tmdb_id, media_type, title}]), tmdb_enriched_at.
- tmdb.py: TmdbClient.fetch_person (/person/{id}+combined_credits), parse_person
  (bio + a popularity-ranked, deduped known_for), apply_person, enrich_person
  (lazy one-shot, key+id guarded, commits, 404 stamps the watermark).
- people.py person_detail: loads the full person row, lazily enriches (best-effort
  — never fails the page), serves the bio fields + resolves known_for to library
  rows by guid (in-library only, popularity order).
- FE PlexPersonView: bio/birth-facts/aka hero + a "Known for" Carousel rail above
  the existing Movies/Shows filmography; PlexPersonDetail type + i18n (en+hu).

Tests: test_plex_person_bio.py (6: parse / lazy-enrich guards / serve) + extended
PlexPersonView.dom.test.tsx + the unknown-name contract in test_plex_person.py.
Browser-E2E'd on Jim Carrey (live TMDB enrich → bio 1937 chars, born 1962-01-17
Newmarket, Known-for resolved). Gate: vitest 337, backend lane 402.

backend/app/models.py

@@ -1259,6 +1259,18 @@ class PlexPerson(Base, TimestampMixin, UpdatedAtMixin):
     # TMDB person id, linked by name from a title's TMDB credits (E5 S2 lays the foundation; the /person
     # biography fetch + person-page render land in S6). NULL until a TMDB-enriched title names this person.
     tmdb_person_id: Mapped[int | None] = mapped_column(Integer)
+    # --- TMDB person enrichment (E5 S6): fetched from /person/{tmdb_person_id} the first time the person
+    #     page is opened, then SERVED FROM THE ROW. `tmdb_enriched_at` is the watermark (set even on a
+    #     no-op fetch so it isn't retried every open). `known_for` = top combined-credits [{tmdb_id,
+    #     media_type, title}], resolved to library rows by guid at serve time (like recommendations). ---
+    biography: Mapped[str | None] = mapped_column(Text)
+    birthday: Mapped[str | None] = mapped_column(String(10))  # "YYYY-MM-DD", served as-is
+    deathday: Mapped[str | None] = mapped_column(String(10))
+    place_of_birth: Mapped[str | None] = mapped_column(Text)
+    known_for_department: Mapped[str | None] = mapped_column(String(64))
+    also_known_as: Mapped[list | None] = mapped_column(JSONB(none_as_null=True))  # [str]
+    known_for: Mapped[list | None] = mapped_column(JSONB(none_as_null=True))  # [{tmdb_id, media_type, title}]
+    tmdb_enriched_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
 
 
 class PlexCollection(Base, TimestampMixin, UpdatedAtMixin):