feat(plex): S4 actor detail page — filmography endpoint + person subview

Backend: new GET /api/plex/person/{name} returns a cast/crew member's cached headshot plus
the movies (PlexItem, kind=movie) and shows (PlexShow) in the enabled libraries whose
cast_names OR directors include the name — the inverse of the cast → filter link. Introduce a
shared _content_libs(db) helper (enabled-library partition) and reuse it in people_cards;
S5 will extend it with the HU-overlay exclusion. Watch-state comes from PlexState / rollup
(reusing _movie_card / _show_card / state_map). DB-lane tests cover cast+director credits,
library scoping, the kind filter, unknown-name empties, and the partition helper.

Frontend: a new `person` history-subview. A cast-row click (PlexInfo cast row + the show
page's CastStrip) now opens the person's filmography page instead of filtering; the filter
gesture moves to a "Filter library by {name}" button on the page itself. PlexPersonView
mirrors PlexInfoView's fetch-wrapper + glass hero (headshot + name + credit counts) and
renders Movies / Shows as PlexPosterCard grids, with an optimistic per-card watch toggle on
the person cache. New plexPerson query key + api client + PlexPersonDetail type; HU/EN copy.

frontend/src/components/PlexInfo.tsx

@@ -31,6 +31,8 @@ type Props = {
   // When provided, metadata (year/genre/director/cast/studio/rating) becomes clickable and sets
   // the corresponding Plex filter (then the opener navigates to the filtered grid).
   onFilter?: (patch: Partial<PlexFilters>) => void;
+  // When provided, a cast member's photo/name opens their filmography page instead of filtering.
+  onOpenPerson?: (name: string) => void;
   // Play a sibling title from a collection strip (opens its player).
   onPlayItem?: (id: string) => void;
   // The item's library key — enables the admin "Manage collections" editor (page variant, movies).
@@ -44,6 +46,7 @@ export default function PlexInfo({
   onClose,
   onStateChange,
   onFilter,
+  onOpenPerson,
   onPlayItem,
   library,
 }: Props) {
@@ -341,12 +344,13 @@ export default function PlexInfo({
             </h2>
             <div className="flex gap-3 overflow-x-auto pb-2">
               {cast.map((c, i) => {
+                const clickable = !!(onOpenPerson || onFilter);
                 const inner = (
                   <>
                     <div
                       className={`mx-auto mb-1 h-20 w-20 overflow-hidden rounded-full border ${
                         overlay ? "border-white/15 bg-white/10" : "border-border bg-surface"
-                      } ${onFilter ? "group-hover/cast:border-accent" : ""}`}
+                      } ${clickable ? "group-hover/cast:border-accent" : ""}`}
                     >
                       {c.thumb ? (
                         <img src={c.thumb} alt="" className="h-full w-full object-cover" />
@@ -358,7 +362,7 @@ export default function PlexInfo({
                     </div>
                     <div
                       className={`truncate text-xs font-medium ${overlay ? "text-white/90" : ""} ${
-                        onFilter ? "group-hover/cast:text-accent" : ""
+                        clickable ? "group-hover/cast:text-accent" : ""
                       }`}
                     >
                       {c.name}
@@ -372,11 +376,17 @@ export default function PlexInfo({
                     )}
                   </>
                 );
-                return onFilter ? (
+                return clickable ? (
                   <button
                     key={i}
-                    onClick={() => onFilter({ actors: [c.name] })}
-                    title={t("plex.info.filterActor", { name: c.name })}
+                    onClick={() =>
+                      onOpenPerson ? onOpenPerson(c.name) : onFilter?.({ actors: [c.name] })
+                    }
+                    title={
+                      onOpenPerson
+                        ? t("plex.info.viewPerson", { name: c.name })
+                        : t("plex.info.filterActor", { name: c.name })
+                    }
                     className="group/cast w-20 shrink-0 text-center"
                   >
                     {inner}